Heterogeneous catalysts

ABSTRACT

Heterogeneous catalysts with optional dopants are provided. The catalysts are useful in a variety of catalytic reactions, for example, the oxidative coupling of methane to C 2+  hydrocarbons. Related methods for use and manufacture of the same are also disclosed.

BACKGROUND Technical Field

This invention is generally related to novel heterogeneous catalystsand, more specifically, to heterogeneous catalysts useful in a varietyof catalytic reactions, such as the oxidative coupling of methane to C₂₊hydrocarbons.

Description of the Related Art

Catalysis is the process in which the rate of a chemical reaction iseither increased or decreased by means of a catalyst. Positive catalystsincrease the speed of a chemical reaction, while negative catalysts slowit down. Substances that increase the activity of a catalyst arereferred to as promoters or activators, and substances that deactivate acatalyst are referred to as catalytic poisons or deactivators. Unlikeother reagents, a catalyst is not consumed by the chemical reaction, butinstead participates in multiple chemical transformations. In the caseof positive catalysts, the catalytic reaction generally has a lowerrate-limiting free energy change to the transition state than thecorresponding uncatalyzed reaction, resulting in an increased reactionrate at the same temperature. Thus, at a given temperature, a positivecatalyst tends to increase the yield of desired product while decreasingthe yield of undesired side products. Although catalysts are notconsumed by the reaction itself, they may be inhibited, deactivated ordestroyed by secondary processes, resulting in loss of catalyticactivity.

Catalysts are generally characterized as either heterogeneous orhomogeneous. Heterogeneous catalysts exist in a different phase than thereactants (e.g., a solid metal catalyst and gas phase reactants), andthe catalytic reaction generally occurs on the surface of theheterogeneous catalyst. Thus, for the catalytic reaction to occur, thereactants must diffuse to and/or adsorb onto the catalyst surface. Thistransport and adsorption of reactants is often the rate limiting step ina heterogeneous catalysis reaction. Heterogeneous catalysts are alsogenerally easily separable from the reaction mixture by commontechniques such as filtration or distillation.

In contrast to a heterogeneous catalyst, a homogenous catalyst exists inthe same phase as the reactants (e.g., a soluble organometallic catalystand solvent-dissolved reactants). Accordingly, reactions catalyzed by ahomogeneous catalyst are controlled by different kinetics than aheterogeneously catalyzed reaction. In addition, homogeneous catalystscan be difficult to separate from the reaction mixture.

While catalysis is involved in a number of different technologies, oneparticular area of importance is the petrochemical industry. At thefoundation of the modern petrochemical industry is the energy-intensiveendothermic steam cracking of crude oil. Cracking is used to producenearly all the fundamental chemical intermediates in use today. Theamount of oil used for cracking and the volume of greenhouse gases (GHG)emitted in the process are quite large: cracking consumes nearly 10% ofthe total oil extracted globally and produces 200M metric tons of CO₂equivalent every year (Ren, T, Patel, M. Res. Conserv. Recycl. 53:513,2009). There remains a significant need in this field for new technologydirected to the conversion of unreactive petrochemical feedstocks (e.g.,paraffins, methane, ethane, etc.) into reactive chemical intermediates(e.g., olefins), particularly with regard to highly selectiveheterogeneous catalysts for the direct oxidation of hydrocarbons.

While there are multistep paths to convert methane to certain specificchemicals using first; high temperature steam reforming to syngas (amixture of H₂ and CO), followed by stoichiometry adjustment andconversion to either methanol or, via the Fischer-Tropsch (F-T)synthesis, to liquid hydrocarbon fuels such as diesel or gasoline, thisdoes not allow for the formation of certain high value chemicalintermediates. This multi-step indirect method also requires a largecapital investment in facilities and is expensive to operate, in partdue to the energy intensive endothermic reforming step. For instance, inmethane reforming, nearly 40% of methane is consumed as fuel for thereaction. It is also inefficient in that a substantial part of thecarbon fed into the process ends up as the GHG CO₂, both directly fromthe reaction and indirectly by burning fossil fuels to heat thereaction. Thus, to better exploit the natural gas resource, directmethods that are more efficient, economical and environmentallyresponsible are required.

One of the reactions for direct natural gas activation and itsconversion into a useful high value chemical, is the oxidative couplingof methane (“OCM”) to ethylene: 2CH₄+O₂→C₂H₄+2H₂O. See, e.g., Zhang, Q.,Journal of Natural Gas Chem., 12:81, 2003; Olah, G. “HydrocarbonChemistry”, Ed. 2, John Wiley & Sons (2003). This reaction is exothermic(ΔH=−67 kcals/mole) and has typically been shown to occur at very hightemperatures (>700° C.). Although the detailed reaction mechanism is notfully characterized, experimental evidence suggests that free radicalchemistry is involved. (Lunsford, J. Chem. Soc., Chem. Comm., 1991; H.Lunsford, Angew. Chem., Int. Ed. Engl., 34:970, 1995). In the reaction,methane (CH₄) is activated on the catalyst surface, forming methylradicals which then couple in the gas phase to form ethane (C₂H₆),followed by dehydrogenation to ethylene (C₂H₄). Several catalysts, withand without dopants, have shown activity for OCM; however, none of thesecatalysts have shown sufficient activity for commercial-scaleimplementation of OCM.

Since the OCM reaction was first reported over thirty years ago, it hasbeen the target of intense scientific and commercial interest, but thefundamental limitations of the conventional approach to C—H bondactivation appear to limit the yield of this attractive reaction.Specifically, numerous publications from industrial and academic labshave consistently demonstrated characteristic performance of highselectivity at low conversion of methane, or low selectivity at highconversion (J. A. Labinger, Cat. Left., 1:371, 1988). Limited by thisconversion/selectivity threshold, no OCM catalyst has been able toexceed 20-25% combined C₂ yield (i.e., ethane and ethylene), and moreimportantly, all such reported yields operate at extremely hightemperatures (>800 C).

In this regard, it is believed that the low yield of desired products(i.e., C₂H₄ and C₂H₆) is caused by the unique homogeneous/heterogeneousnature of the reaction. Specifically, due to the high reactiontemperature, a majority of methyl radicals escape the catalyst surfaceand enter the gas phase. There, in the presence of oxygen and hydrogen,multiple side reactions are known to take place (J. A. Labinger, Cat.Lett., 1:371, 1988). The non-selective over-oxidation of hydrocarbons toCO and CO₂ (e.g., complete oxidation) is the principal competing fastside reaction. Other undesirable products (e.g., methanol, formaldehyde)have also been observed and rapidly react to form CO and CO₂.

In order to result in a commercially viable OCM process, a catalystoptimized for the activation of the C—H bond of methane at lowertemperatures (e.g., 500-800° C.) higher activities, and higher pressuresare required. While the above discussion has focused on the OCMreaction, numerous other catalytic reactions (as discussed in greaterdetail below) would significantly benefit from catalytic optimization.Accordingly, there remains a need in the art for improved catalysts and,more specifically, catalysts for improving the yield, selectivity andconversion of, for example, the OCM reaction and other catalyzedreactions. The present invention fulfills these needs and providesfurther related advantages.

BRIEF SUMMARY

In brief, heterogeneous metal oxide catalysts and related methods aredisclosed. For example, catalysts comprising oxides of one or morelanthanide elements and optional dopants are provided in variousembodiments. The disclosed catalysts find utility in any number ofcatalytic reactions, for example in the OCM reaction. In someembodiments, the catalysts are advantageously doped with one or moredoping elements. The doping elements may be promoters such that thecatalyst comprises an improved catalytic activity. For example, incertain embodiments, the catalytic activity is such that the C₂₊selectivity is 50% or greater and the methane conversion is 20% orgreater when the catalyst is employed as a heterogeneous catalyst in theoxidative coupling of methane at a temperature of 850° C. or less, 800°C. or less, for example 750° C. or less or 700° C. or less.

Methods for use of the disclosed catalysts in catalytic reactions, forexample OCM, are also provided. Furthermore, the present disclosure alsoprovides for the preparation of downstream products of ethylene, whereinthe ethylene has been prepared via a reaction employing a catalystdisclosed herein.

These and other aspects of the invention will be apparent upon referenceto the following detailed description. To this end, various referencesare set forth herein which describe in more detail certain backgroundinformation, procedures, compounds and/or compositions, and are eachhereby incorporated by reference in their entirety.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the drawings, the sizes and relative positions of elements in thedrawings are not necessarily drawn to scale. For example, the variouselements and angles are not drawn to scale, and some of these elementsare arbitrarily enlarged and positioned to improve drawing legibility.Further, the particular shapes of the elements as drawn are not intendedto convey any information regarding the actual shape of the particularelements, and have been selected solely for ease of recognition in thedrawings.

FIG. 1 schematically depicts a first part of an OCM reaction at thesurface of a metal oxide catalyst.

FIG. 2 shows a method for catalyst screening.

FIG. 3 schematically depicts a carbon dioxide reforming reaction on acatalytic surface.

FIG. 4 is a flow chart for data collection and processing in evaluatingcatalytic performance.

FIG. 5 is a chart showing various downstream products of ethylene.

FIG. 6 shows an OCM and ethylene oligomerization module.

FIGS. 7A and 7B show scanning electron micrographs of representativecatalysts.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various embodiments.However, one skilled in the art will understand that the invention maybe practiced without these details. In other instances, well-knownstructures have not been shown or described in detail to avoidunnecessarily obscuring descriptions of the embodiments. Unless thecontext requires otherwise, throughout the specification and claimswhich follow, the word “comprise” and variations thereof, such as,“comprises” and “comprising” are to be construed in an open, inclusivesense, that is, as “including, but not limited to.” Further, headingsprovided herein are for convenience only and do not interpret the scopeor meaning of the claimed invention.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments. Also, as used in thisspecification and the appended claims, the singular forms “a,” “an,” and“the” include plural referents unless the content clearly dictatesotherwise. It should also be noted that the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

As discussed above, heterogeneous catalysis takes place between at leasttwo phases. Generally, the catalyst is a solid, the reactants are gasesor liquids and the products are gases or liquids. While not wishing tobe bound by theory, it is believed that a heterogeneous catalystprovides a surface that has multiple active sites for adsorption of onemore gas or liquid reactants. Once adsorbed, certain bonds within thereactant molecules are weakened and dissociate, creating reactivefragments of the reactants, e.g., in free radical forms. One or moreproducts are generated as new bonds between the resulting reactivefragments form, in part, due to their proximity to each other on thecatalytic surface.

As an example, FIG. 1 shows schematically a theoretical representationof the first part of an OCM reaction that takes place on the surface ofan exemplary metal oxide catalyst 10 which is followed by methyl radicalcoupling in the gas phase. A crystal lattice structure of metal atoms 14and oxygen atoms 20 are shown, with an optional dopant 24 incorporatedinto the lattice structure. In this reaction, a methane molecule 28comes into contact with an active site (e.g., surface oxygen 30) andbecomes activated when a hydrogen atom 34 dissociates from the methanemolecule 28. As a result, a methyl radical 40 is generated on or nearthe catalytic surface. Two methyl radicals thus generated can couple inthe gas phase to create ethane and/or ethylene, which are collectivelyreferred to as the “C2” coupling products.

It is generally recognized that the catalytic properties of a catalyststrongly correlate to its surface morphology. Typically, the surfacemorphology can be defined by geometric parameters such as: (1) thenumber of surface atoms (e.g., the surface oxygen of FIG. 1) thatcoordinate to the reactant; and (2) the degree of coordinativeunsaturation of the surface atoms, which is the coordination number ofthe surface atoms with their neighboring atoms. For example, thereactivity of a surface atom decreases with decreasing coordinativeunsaturation. For example, for the dense surfaces of a face-centeredcrystal, a surface atom with 9 surface atom neighbors will have adifferent reactivity than one with 8 neighbors. Additional surfacecharacteristics that may contribute to the catalytic properties include,for example, crystal dimensions, lattice distortion, surfacereconstructions, defects, grain boundaries, and the like. See, e.g., VanSanten R. A. et al New Trends in Materials Chemistry 345-363 (1997).

Advantageously, embodiments of the catalysts disclosed herein andmethods of producing the same have general applicability to a widevariety of heterogeneous catalyses, including without limitation:oxidative coupling of methane (e.g., FIG. 1), oxidative dehydrogenationof alkanes to their corresponding alkenes, selective oxidation ofalkanes to alkenes and alkynes, oxidation of carbon monoxide, dryreforming of methane, selective oxidation of aromatics, Fischer-Tropschreaction, hydrocarbon cracking, combustion of hydrocarbons and the like.

FIG. 2 schematically shows an exemplary high throughput work flow forgenerating libraries of diverse catalysts and screening for theircatalytic properties. An initial phase of the work flow involves aprimary screening, which is designed to broadly and efficiently screen alarge and diverse set of catalysts that logically could perform thedesired catalytic transformation. For example, certain doped metaloxides (e.g., Mn, Mg, W, etc.) are known catalysts for the OCM reaction.Therefore, catalysts of various metal oxide compositions comprisingvarious dopants can be prepared and evaluated for their catalyticperformances in an OCM reaction.

More specifically, the work flow 100 begins with designing syntheticexperiments for making various metal oxide compositions (block 110). Thesynthesis, subsequent treatments and screenings can be manual orautomated. As will be discussed in more detail herein, by varying thesynthetic conditions, catalysts can be prepared with various surfacemorphologies and/or compositions in respective microwells (block 114).The catalysts are subsequently calcined and optionally doped (block120). As discussed in more detail herein, the optional dopants may beincorporated during preparation of the catalysts (114) or as a separatestep after preparation of the catalysts and before or after calcination.Optionally, the catalysts are further mixed with a catalyst support(block 122). As with the dopant, the optional support can also beincorporated at any point in the preparation of the catalysts, and itsincorporation is not limited by the depicted order in FIG. 2.

Beyond the optional support step, all subsequent steps are carried outin a “wafer” format, in which catalysts are deposited in a quartz waferthat has been etched to create an ordered array of microwells. Eachmicrowell is a self-contained reactor, in which independently variableprocessing conditions can be designed to include, without limitation,respective choices of elemental compositions, catalyst support, reactionprecursors, templates, reaction durations, pH values, temperatures,ratio between reactants, gas flows, and calcining conditions (block124). Due to design constraints of some wafers, in some embodimentscalcining and other temperature variables are identical in allmicrowells. A wafer map 130 can be created to correlate the processingconditions to the catalyst in each microwell. A library of diversecatalysts can be generated in which each library member corresponds to aparticular set of processing conditions and corresponding compositionaland/or morphological characteristics.

Catalysts obtained under various synthetic conditions and dopingcompositions are thereafter deposited in respective microwells of awafer (140) for evaluating their respective catalytic properties in agiven reaction (blocks 132 and 134). The catalytic performance of eachlibrary member can be screened serially by several known primaryscreening technologies, including scanning mass spectroscopy (SMS)(Symyx Technologies Inc., Santa Clara, Calif.). The screening process isfully automated, and the SMS tool can determine if a catalyst iscatalytically active or not, as well as its relative strength as acatalyst at a particular temperature. Typically, the wafer is placed ona motion control stage capable of positioning a single well below aprobe that flows the feed of the starting material over the catalystsurface and removes reaction products to a mass spectrometer and/orother detector technologies (blocks 134 and 140). The individualcatalyst is heated to a preset reaction temperature, e.g., using a CO₂IR laser from the backside of the quartz wafer and an IR camera tomonitor temperature and a preset mixture of reactant gases. The SMS toolcollects data with regard to the consumption of the reactant(s) and thegeneration of the product(s) of the catalytic reaction in each well(block 144), and at each temperature and flow rate.

The SMS data obtained as described above provide information on relativecatalytic properties among all the library members (block 150). In orderto obtain more quantitative data on the catalytic properties of thecatalysts, possible hits that meet certain criteria are subjected to asecondary screening (block 154). Typically, secondary screeningtechnologies include a single, or alternatively multiple channelfixed-bed or fluidized bed reactors (as described in more detailherein). In parallel reactor systems or multi-channel fixed-bed reactorsystem, a single feed system supplies reactants to a set of flowrestrictors. The flow restrictors divide the flows evenly among parallelreactors. Care is taken to achieve uniform reaction temperature betweenthe reactors such that the various catalysts can be differentiatedsolely based on their catalytic performances. The secondary screeningallows for accurate determination of catalytic properties such asselectivity, yield and conversion (block 160). These results serve as afeedback for designing further catalyst libraries.

Secondary screening is also schematically depicted in FIG. 4, whichdepicts a flow chart for data collection and processing in evaluatingcatalytic performance of catalysts according to the invention.Additional description of SMS tools in a combinatorial approach fordiscovering catalysts can be found in, e.g., Bergh, S. et al. Topics inCatalysts 23:1-4, 2003.

Thus, in accordance with various embodiments described herein,compositional and morphologically diverse catalysts can be rationallysynthesized to meet catalytic performance criteria. These and otheraspects of the present disclosure are described in more detail below.

Definitions

As used herein, and unless the context dictates otherwise, the followingterms have the meanings as specified below.

“Catalyst” means a substance which alters the rate of a chemicalreaction. A catalyst may either increase the chemical reaction rate(i.e., a “positive catalyst”) or decrease the reaction rate (i.e., a“negative catalyst”). Catalysts participate in a reaction in a cyclicfashion such that the catalyst is cyclically regenerated. “Catalytic”means having the properties of a catalyst.

“Turnover number” is a measure of the number of reactant molecules acatalyst can convert to product molecules per unit time.

“Active” or “catalytically active” refers to a catalyst which hassubstantial activity in the reaction of interest. For example, in someembodiments a catalyst which is OCM active (i.e., has activity in theOCM reaction) has a C2+ selectivity of 5% or more and/or a methaneconversion of 5% or more when the catalyst is employed as aheterogeneous catalyst in the oxidative coupling of methane at atemperature of 750° C. or less.

“Inactive” or “catalytically inactive” refers to a catalyst which doesnot have substantial activity in the reaction of interest. For example,in some embodiments a catalyst which is OCM inactive has a C2+selectivity of less than 5% and/or a methane conversion of less than 5%when the catalyst is employed as a heterogeneous catalyst in theoxidative coupling of methane at a temperature of 750° C. or less.

“Activation temperature” refers to the temperature at which a catalystbecomes catalytically active.

“OCM activity” refers to the ability of a catalyst to catalyze the OCMreaction.

A catalyst having “high OCM activity” refers to a catalyst having a C2+selectivity of 50% or more and/or a methane conversion of 20% or morewhen the catalyst is employed as a heterogeneous catalyst in theoxidative coupling of methane at a specific temperature, for example750° C. or less.

A catalyst having “moderate OCM activity” refers to a catalyst having aC2+ selectivity of about 20-50% and/or a methane conversion of about10-20% or more when the catalyst is employed as a heterogeneous catalystin the oxidative coupling of methane at a temperature of 750° C. orless.

A catalyst having “low OCM activity” refers to a catalyst having a C2+selectivity of about 5-20% and/or a methane conversion of about 5-10% ormore when the catalyst is employed as a heterogeneous catalyst in theoxidative coupling of methane at a temperature of 750° C. or less.

“Base material” refers to the major component of a catalyst. For examplea mixed oxide of manganese and magnesium which is doped with lithiumand/or boron comprises a manganese/magnesium oxide base material.

“Dopant” or “doping agent” or “doping element” is a chemical element (orin some embodiments a compound) which is added to or incorporated withina catalyst base material to optimize catalytic performance (e.g.,increase or decrease catalytic activity). As compared to the undopedcatalyst, a doped catalyst may increase or decrease the selectivity,conversion, and/or yield of a reaction catalyzed by the catalyst.Dopants which increase catalytic activity are referred to as “promoters”while dopants which decrease catalytic activity are referred to as“poisons”. For example, a promoter with respect to a certain reaction(e.g., OCM) refers to a dopant which increases the catalytic activity ofthe catalyst (relative to undoped catalyst) in the reaction. In someembodiments, an increase in catalytic activity is evidenced by any oneor more of: an increase in yield (e.g., C2+ yield), an increase inselectivity (e.g., C2+ selectivity), and increase in conversion (e.g.,methane conversion) or a decrease in the temperature required tomaintain the same yield, selectivity and/or conversion. The dopant maybe present in the catalyst in any form and may be derived from anysuitable source of the element (e.g., elemental form, chlorides,bromides, iodides, nitrates, oxynitrates, oxyhalides, acetates,formates, hydroxides, carbonates, phosphates, sulfates, alkoxides,oxides and the like.)

“Atomic percent” (at % or at/at) or “atomic ratio” when used in thecontext of catalyst dopants refers to the ratio of the total number ofdopant atoms to the total number of non-oxygen atoms in the basematerial. For example, the atomic percent of dopant in a lithium dopedMg₆MnO₈ catalyst is determined by calculating the total number oflithium atoms and dividing by the sum of the total number of magnesiumand manganese atoms and multiplying by 100 (i.e., atomic percent ofdopant=[Li atoms/(Mg atoms+Mn atoms)]×100).

“Weight percent” (wt/wt)” when used in the context of catalyst dopantsrefers to the ratio of the total weight of dopant to the total combinedweight of the dopant and the catalyst. For example, the weight percentof dopant in a lithium doped Mg₆MnO₈ catalyst is determined bycalculating the total weight of lithium and dividing by the sum of thetotal combined weight of lithium and Mg₆MnO₈ and multiplying by 100(i.e., weight percent of dopant=[Li weight/(Li weight+Mg₆MnO₈weight)]×100).

“Group 1” elements include lithium (Li), sodium (Na), potassium (K),rubidium (Rb), cesium (Cs), and francium (Fr).

“Group 2” elements include beryllium (Be), magnesium (Mg), calcium (Ca),strontium (Sr), barium (Ba), and radium (Ra).

“Group 3” elements include scandium (Sc) and yttrium (Y).

“Group 4” elements include titanium (Ti), zirconium (Zr), halfnium (Hf),and rutherfordium (Rf).

“Group 5” elements include vanadium (V), niobium (Nb), tantalum (Ta),and dubnium (Db).

“Group 6” elements include chromium (Cr), molybdenum (Mo), tungsten (W),and seaborgium (Sg).

“Group 7” elements include manganese (Mn), technetium (Tc), rhenium(Re), and bohrium (Bh).

“Group 8” elements include iron (Fe), ruthenium (Ru), osmium (Os), andhassium (Hs).

“Group 9” elements include cobalt (Co), rhodium (Rh), iridium (Ir), andmeitnerium (Mt).

“Group 10” elements include nickel (Ni), palladium (Pd), platinum (Pt)and darmistadium (Ds).

“Group 11” elements include copper (Cu), silver (Ag), gold (Au), androentgenium (Rg).

“Group 12” elements include zinc (Zn), cadmium (Cd), mercury (Hg), andcopernicium (Cn).

“Group 13” elements include boron (B), aluminum (Al), gallium (Ga),indium (In) and thallium (TI).

“Group 16” elements include oxygen (O), sulfur (S), selenium (Se),tellurium (Te) and polonium (Po).

“Lanthanides” include lanthanum (La), cerium (Ce), praseodymium (Pr),neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu),gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium(Er), thulium (Tm), yitterbium (Yb), and lutetium (Lu).

“Actinides” include actinium (Ac), thorium (Th), protactinium (Pa),uranium (U), neptunium (Np), plutonium (Pu), americium (Am), curium(Cm), berklelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm),mendelevium (Md), nobelium (No), and lawrencium (Lr).

“Rare earth elements” include the lanthanides, actinides and Group 3.

“Metal element” or “metal” is any element, except hydrogen, selectedfrom Groups 1 through 12, lanthanides, actinides, aluminum (Al), gallium(Ga), indium (In), tin (Sn), thallium (TI), lead (Pb), and bismuth (Bi).Metal elements include metal elements in their elemental form as well asmetal elements in an oxidized or reduced state, for example, when ametal element is combined with other elements in the form of compoundscomprising metal elements. For example, metal elements can be in theform of hydrates, salts, oxides, as well as various polymorphs thereof,and the like.

“Semi-metal element” refers to an element selected from boron (B),silicon (Si), germanium (Ge), arsenic (As), antimony (Sb), tellurium(Te), and polonium (Po).

“Non-metal element” refers to an element selected from carbon (C),nitrogen (N), oxygen (O), fluorine (F), phosphorus (P), sulfur (S),chlorine (Cl), selenium (Se), bromine (Br), iodine (I), and astatine(At).

“C2” refers to a hydrocarbon (i.e., compound consisting of carbon andhydrogen atoms) having only two carbon atoms, for example ethane andethylene. Similarly, “C3” refers to a hydrocarbon having only 3 carbonatoms, for example propane and propylene.

“Conversion” means the mole fraction (i.e., percent) of a reactantconverted to a product or products.

“Selectivity” refers to the percent of converted reactant that went to aspecified product, e.g., C2 selectivity is the % of converted methanethat formed ethane and ethylene, C3 selectivity is the % of convertedmethane that formed propane and propylene, C2+ selectivity is the % ofconverted methane that formed ethane, ethylene, propane, propylene andother higher hydrocarbons (hydrocarbons comprising 2 or more carbons).CO selectivity is the % of converted methane that formed CO.

“Yield” is a measure of (e.g., percent) of product obtained relative tothe theoretical maximum product obtainable. Yield is calculated bydividing the amount of the obtained product in moles by the theoreticalyield in moles. Percent yield is calculated by multiplying this value by100. C2 yield is defined as the sum of the ethane and ethylene molarflow at the reactor outlet multiplied by two and divided by the inletmethane molar flow. C3 yield is defined as the sum of propane andpropylene molar flow at the reactor outlet multiplied by three anddivided by the inlet methane molar flow. C2+ yield is the sum of the C2yield and C3 yield and the yield of other higher hydrocarbons shouldthey be present in any measurable quantities. Yield is also calculableby multiplying the methane conversion by the relevant selectivity, e.g.,C2 yield is equal to the methane conversion times the C2 selectivity.C2+ yield is equal to the methane conversion times the C2+ selectivity.

“Bulk catalyst” or “bulk material” means a catalyst prepared bytraditional techniques, for example by milling or grinding largecatalyst particles to obtain smaller/higher surface area catalystparticles.

“Nanostructured catalyst” means a catalyst having at least one dimensionon the order of nanometers (e.g., between about 1 and 100 nanometers).Non-limiting examples of nanostructured catalysts include nanoparticlecatalysts and nanowire catalysts.

“Nanoparticle” means a particle having at least one diameter on theorder of nanometers (e.g., between about 1 and 100 nanometers).

“Nanowire” means a wire-like structure having at least one diameter onthe order of nanometers (e.g., between about 1 and 100 nanometers) andan aspect ratio greater than 10:1. The “aspect ratio” of a nanowire isthe ratio of the actual length (L) of the nanowire to the diameter (D)of the nanowire. Aspect ratio is expressed as L:D. Exemplary nanowiresare known in the art and described in more detail in co-pending U.S.application Ser. No. 13/115,082 (U.S. Pub. No. 2012/0041246), Ser. No.13/689,514 (U.S. Pub. No. 2013/0158322) and Ser. No. 13/689,611 (U.S.Pub. No. 2013/0165728), the full disclosures of which are herebyincorporated by reference in their entireties for all purposes.

“Polycrystalline nanowire” means a nanowire having multiple crystaldomains. Polycrystalline nanowires generally have different morphologies(e.g., bent vs. straight) as compared to the corresponding“single-crystalline” nanowires.

“Crystal domain” means a continuous region over which a substance iscrystalline.

“Single-crystalline nanowire” means a nanowire having a single crystaldomain.

“Effective length” of a nanowire means the shortest distance between thetwo distal ends of a nanowire as measured by transmission electronmicroscopy (TEM) in bright field mode at 5 keV. “Average effectivelength” refers to the average of the effective lengths of individualnanowires within a plurality of nanowires.

“Actual length” of a nanowire means the distance between the two distalends of a nanowire as traced through the backbone of the nanowire asmeasured by TEM in bright field mode at 5 keV. “Average actual length”refers to the average of the actual lengths of individual nanowireswithin a plurality of nanowires.

The “diameter” of a nanowire is measured in an axis perpendicular to theaxis of the nanowire's actual length (i.e., perpendicular to thenanowires backbone). The diameter of a nanowire will vary from narrow towide as measured at different points along the nanowire backbone. Asused herein, the diameter of a nanowire is the most prevalent (i.e., themode) diameter.

The “ratio of effective length to actual length” is determined bydividing the effective length by the actual length. A nanowire having a“bent morphology” will have a ratio of effective length to actual lengthof less than one as described in more detail herein. A straight nanowirewill have a ratio of effective length to actual length equal to one asdescribed in more detail herein.

“Inorganic” means a substance comprising a metal element or semi-metalelement. In certain embodiments, inorganic refers to a substancecomprising a metal element. An inorganic compound can contain one ormore metals in its elemental state, or more typically, a compound formedby a metal ion (M^(n+), wherein n 1, 2, 3, 4, 5, 6 or 7) and an anion(X^(m−), m is 1, 2, 3 or 4), which balance and neutralize the positivecharges of the metal ion through electrostatic interactions.Non-limiting examples of inorganic compounds include oxides, hydroxides,halides, nitrates, sulfates, carbonates, phosphates, acetates, oxalates,and combinations thereof, of metal elements. Other non-limiting examplesof inorganic compounds include Li₂CO₃, Li₂PO₄, LiOH, Li₂O, LiCl, LiBr,LiI, Li₂C₂O₄, Li₂SO₄, Na₂CO₃, Na₂PO₄, NaOH, Na₂O, NaCl, NaBr, NaI,Na₂C₂O₄, Na₂SO₄, K₂CO₃, K₂PO₄, KOH, K₂O, KCl, KBr, KI, K₂C₂O₄, K₂SO₄,Cs₂CO₃, CsPO₄, CsOH, Cs₂O, CsCl, CsBr, CsI, CsC₂O₄, CsSO₄, Be(OH)₂,BeCO₃, BePO₄, BeO, BeCl₂, BeBr₂, BeI₂, BeC₂O₄, BeSO₄, Mg(OH)₂, MgCO₃,MgPO₄, MgO, MgCl₂, MgBr₂, MgI₂, MgC₂O₄, MgSO₄, Ca(OH)₂, CaO, CaCO₃,CaPO₄, CaCl₂, CaBr₂, CaI₂, Ca(OH)₂, CaC₂O₄, CaSO₄, Y₂O₃, Y₂(CO₃)₃,Y₂(PO₄)₃, Y(OH)₃, YCl₃, YBr₃, Y₁₃, Y₂(C₂O₄)₃, Y₂(SO₄)₃, Zr(OH)₄,Zr(CO₃)₂, Zr(PO₄)₂, ZrO(OH)₂, ZrO₂, ZrCl₄, ZrBr₄, ZrI₄, Zr(C₂O₄)₂,Zr(SO₄)₂, Ti(OH)₄, TiO(OH)₂, Ti(CO₃)₂, Ti(PO₄)₂, TiO₂, TiCl₄, TiBr₄,TiI₄, Ti(C₂O₄)₂, Ti(SO₄)₂, BaO, Ba(OH)₂, BaCO₃, BaPO₄, BaCl₂, BaBr₂,BaI₂, BaC₂O₄, BaSO₄, La(OH)₃, La₂(CO₃)₃, La₂(PO₄)₃, La₂O₃, LaCl₃, LaBr₃,LaI₃, La₂(C₂O₄)₃, La₂(SO₄)₃, Ce(OH)₄, Ce(CO₃)₂, Ce(PO₄)₂, CeO₂, Ce₂O₃,CeCl₄, CeBr₄, CeI₄, Ce(C₂O₄)₂, Ce(SO₄)₂, ThO₂, Th(CO₃)₂, Th(PO₄)₂,ThCl₄, ThBr₄, ThI₄, Th(OH)₄, Th(C₂O₄)₂, Th(SO₄)₂, Sr(OH)₂, SrCO₃, SrPO₄,SrO, SrCl₂, SrBr₂, SrI₂, SrC₂O₄, SrSO₄, Sm₂O₃, Sm₂(CO₃)₃, Sm₂(PO₄)₃,SmCl₃, SmBr₃, SmI₃, Sm(OH)₃, Sm₂(CO₃)₃, Sm₂(C₂O₃)₃, Sm₂(SO₄)₃,LiCa₂Bi₃O₄C₁₆, Na₂WO₄, K/SrCoO₃, K/Na/SrCoO₃, Li/SrCoO₃, SrCoO₃,molybdenum oxides, molybdenum hydroxides, molybdenum carbonates,molybdenum phosphates, molybdenum chlorides, molybdenum bromides,molybdenum iodides, molybdenum oxalates, molybdenum sulfates, manganeseoxides, manganese chlorides, manganese bromides, manganese iodides,manganese hydroxides, manganese oxalates, manganese sulfates, manganesetungstates, vanadium oxides, vanadium carbonates, vanadium phosphates,vanadium chlorides, vanadium bromides, vanadium iodides, vanadiumhydroxides, vanadium oxalates, vanadium sulfates, tungsten oxides,tungsten carbonates, tungsten phosphates, tungsten chlorides, tungstenbromides, tungsten iodides, tungsten hydroxides, tungsten oxalates,tungsten sulfates, neodymium oxides, neodymium carbonates, neodymiumphosphates, neodymium chlorides, neodymium bromides, neodymium iodides,neodymium hydroxides, neodymium oxalates, neodymium sulfates, europiumoxides, europium carbonates, europium phosphates, europium chlorides,europium bromides, europium iodides, europium hydroxides, europiumoxalates, europium sulfates rhenium oxides, rhenium carbonates, rheniumphosphates, rhenium chlorides, rhenium bromides, rhenium iodides,rhenium hydroxides, rhenium oxalates, rhenium sulfates, chromium oxides,chromium carbonates, chromium phosphates, chromium chlorides, chromiumbromides, chromium iodides, chromium hydroxides, chromium oxalates,chromium sulfates, potassium molybdenum oxides and the like.

“Salt” means a compound comprising negative and positive ions. Salts aregenerally comprised of cations and counter ions. Under appropriateconditions, e.g., the solution also comprises a template, the metal ion(M^(n+)) and the anion (X^(m−)) bind to the template to inducenucleation and growth of a nanowire of M_(m)X_(n) on the template.“Anion precursor” thus is a compound that comprises an anion and acationic counter ion, which allows the anion (X^(m−)) to dissociate fromthe cationic counter ion in a solution.

“Oxide” generally refers to an oxidized element (i.e., oxidation stategreater than 0). Oxides generally comprise oxygen. Examples of oxidesinclude, but are not limited to oxidized metals such as, metal oxides(M_(x)O_(y)), metal oxyhalides (M_(x)O_(y)X_(z)), metal oxynitrates(M_(x)O_(y)(NO₃)_(z)), metal phosphates (M_(x)(PO₄)_(y)), metaloxycarbonates (M_(x)O_(y)(CO₃)_(z)), metal carbonates, metaloxyhydroxides (M_(x)O_(y)(OH)_(z)) and the like, wherein X isindependently, at each occurrence, fluoro, chloro, bromo or iodo, and x,y and z are numbers from 1 to 100. For purpose of simplicity, theforegoing exemplary oxides are illustrated with one metal (M); however,it should be noted that in certain embodiments oxides will include morethan one metal. The additional metal(s) may be present as part of thebase material and/or as a doping element.

“Catalytic material” refers to a plurality of catalyst particles, whichmay optionally be combined with a support, diluent and/or binder.

“Catalyst form” or “catalytic form” refers to the physical shape of acatalytic material. For example, catalyst forms include catalysts in theshape of extrudates or pellets or disposed on various supportstructures, including honeycomb structures, grids, monoliths, and thelike, as discussed in more detail below.

“Catalyst formulation” or “catalytic formulation” refers to the chemicalcomposition of a catalytic material. For example, a catalyst formulationmay include a catalyst and one or more support, diluent and/or bindermaterials.

An “extrudate” refers to a material (e.g., catalytic material) preparedby forcing a semisolid material comprising a catalyst through a die oropening of appropriate shape. Extrudates can be prepared in a variety ofshapes and structures by common means known in the art.

A “formed aggregate” refers to an aggregation of catalyst materialparticles, either alone, or in conjunction with one or more othermaterials, e.g., catalyst materials, dopants, diluents, supportmaterials, binders, etc., formed into a single particle. Formedaggregates include without limitation, extruded particles, termed“extrudates”, pressed or cast particles, e.g., pellets such as tablets,ovals, spherical particles, etc., coated particles, e.g., spray,immersion or pan coated particles, impregnated particles, e.g.,monoliths, foils, foams, honeycombs, or the like. Formed aggregates mayrange in size from particles having individual cross sections in themicron range to cross sections in the millimeter range, to even largerparticles such as monolithic formed aggregates, that may be on the orderof centimeters or even meters in cross section.

A “pellet” or “pressed pellet” refers to a material (e.g., catalyticmaterial) prepared by applying pressure to (i.e., compressing) amaterial comprising a catalyst into a desired shape. Pellets havingvarious dimensions and shapes can be prepared according to commontechniques in the art.

“Monolith” or “monolith support” is generally a structure formed from asingle structural unit preferably having passages disposed through it ineither an irregular or regular pattern with porous or non-porous wallsseparating adjacent passages. Examples of such monolithic supportsinclude, e.g., ceramic or metal foam-like or porous structures. Thesingle structural unit may be used in place of or in addition toconventional particulate or granular catalysts (e.g., pellets orextrudates). Examples of such irregular patterned monolith substratesinclude filters used for molten metals. Monoliths generally have aporous fraction, for example ranging from about 60% to 90%, and a flowresistance substantially less than the flow resistance of a packed bedof similar volume (e.g., about 10% to 30% of the flow resistance of apacked bed of similar volume). Examples of regular patterned substratesinclude monolith honeycomb supports used for purifying exhausts frommotor vehicles and used in various chemical processes and ceramic foamstructures having irregular passages. Many types of monolith supportstructures made from conventional refractory or ceramic materials suchas alumina, zirconia, yttria, silicon carbide, and mixtures thereof, arewell known and commercially available from, among others, Corning, lac.;Vesuvius Hi-Tech Ceramics, Inc.; and Porvair Advanced Materials, Inc.and SiCAT (Sicatalyst.com). Monoliths include foams, honeycombs, foils,mesh, gauze and the like.

“Alkane” means a straight chain or branched, noncyclic or cyclic,saturated aliphatic hydrocarbon. Representative straight chain alkanesinclude methane, ethane, n-propane, n-butane, n-pentane, n-hexane, andthe like; while branched alkanes include isopropane, sec-butane,isobutane, tert-butane, isopentane, and the like. Representative cyclicalkanes include cyclopropane, cyclobutane, cyclopentane, cyclohexane,and the like.

“Alkene” means a straight chain or branched, noncyclic or cyclic,unsaturated aliphatic hydrocarbon having at least one carbon-carbondouble bond. Representative straight chain and branched alkenes includeethylene, propylene, 1-butene, 2-butene, isobutene, 1-pentene,2-pentene, 3-methyl-1-butene, 2-methyl-2-butene, 2,3-dimethyl-2-butene,and the like. Cyclic alkenes include cyclohexene and cyclopentene andthe like.

“Alkyne” means a straight chain or branched, noncyclic or cyclic,unsaturated aliphatic hydrocarbon having at least one carbon-carbontriple bond. Representative straight chain and branched alkynes includeacetylene, propyne, 1-butyne, 2-butyne, 1-pentyne, 2-pentyne,3-methyl-1-butyne, and the like. Representative cyclic alkynes includecycloheptyne and the like.

“Alkyl,” “alkenyl” and “alkynyl” refer to an alkane, alkene or alkyneradical, respectively.

“Aromatic” means a cyclic moiety (e.g., carbocyclic) having a cyclicsystem of conjugated p orbitals. Representative examples of aromaticsinclude benzene, naphthalene and toluene.

“Carbon-containing compounds” are compounds which comprise carbon.Non-limiting examples of carbon-containing compounds includehydrocarbons, such as methane, ethane and ethylene, CO and CO₂.

“Mixed oxide” or “mixed metal oxide” refers to a catalyst comprising atleast two different oxidized metals. In various embodiments, the mixedoxides are “physical blends” of different oxidized metals. For example,in some embodiments, the mixed oxides are represented byM1_(x)O_(z1)/M2_(y)O_(z2), wherein M1 and M2 are the same or differentmetal elements, O is oxygen and x, y, z1 and z2 are numbers from 1 to100 to 100 and the “/” indicates that the two oxidized metals are incontact (e.g., physically blended) but not necessarily bound via acovalent or ionic or other type of bond. In other examples, a mixedoxide is a compound comprising two or more oxidized metals and oxygen(e.g., M1_(x)M2_(y)O_(z), wherein M1 and M2 are the same or differentmetal elements, O is oxygen and x, y and z are numbers from 1 to 100).

A mixed oxide may comprise metal elements in various oxidation statesand may comprise more than one type of metal element. For example, amixed oxide of manganese and magnesium comprises oxidized forms ofmagnesium and manganese. Each individual manganese and magnesium atommay or may not have the same oxidation state. Mixed oxides comprising 3,4, 5, 6 or more metal elements can be represented in an analogousmanner. Mixed oxides include, but are not limited to metal oxides(M_(x)O_(y)), metal oxyhalides (M_(x)O_(y)X_(z)), metal oxynitrates(M_(x)O_(y)(NO₃)_(z)), metal phosphates (M_(x)(PO₄)_(y)), metaloxycarbonates (M_(x)O_(y)(CO₃)_(z)), metal carbonates, metaloxyhydroxides (M_(x)O_(y)(OH)_(z)) and the like, and combinationsthereof, wherein X is independently, at each occurrence, fluoro, chloro,bromo or iodo, and x, y and z are numbers from 1 to 100. Mixed oxidesmay be represented herein as M1-M2, wherein M1 and M2 are eachindependently a metal element and M1 and M2 are oxidized. Mixed oxidescomprising, 3, 4, 5, 6 or more metal elements can be represented in ananalogous manner.

“Rare earth oxide” refers to an oxide of an element from group 3,lanthanides or actinides. Rare earth oxides include mixed oxidecontaining a rare earth element. Examples of rare earth oxides include,but are not limited to, La₂O₃, Nd₂O₃, Yb₂O₃, Eu₂O₃, Sm₂O₃, Y₂O₃, Ce₂O₃,Pr₂O₃, Ln1_(4-x)Ln2_(x)O₆, La_(4-x)Ln1_(x)O₆, La_(4-x)Nd_(x)O₆, whereinLn1 and Ln2 are each independently a lanthanide element, wherein Ln1 andLn2 are not the same and x is a number ranging from greater than 0 toless than 4, La₃Nd₀₆, LaNd₃O₆, La_(1.5)Nd_(2.5)O₆, La_(2.5)Nd_(1.5)O₆,La_(3.2)Nd_(0.8)O₆, La_(3.5)Nd_(0.5)O₆, La_(3.8)Nd_(0.2)O₆, Y—La, Zr—La,Pr—La and Ce—La.

“O₂-OCM catalyst” refers to a catalyst having activity in the OCMreaction and which predominately uses O₂ as an oxygen source.

“CO₂-OCM catalyst” refers to a catalyst having activity in the OCMreaction and which predominately uses CO₂ as an oxygen source.

“O₂-ODH catalyst” refers to a catalyst having activity in the ODHreaction and which predominately uses O₂ as an oxygen source.

“CO₂-ODH catalyst” refers to a catalyst having activity in the ODHreaction and which predominately uses CO₂ as an oxygen source.

Catalysts

1. Molecular Composition of the Catalysts

As noted above, disclosed herein are catalysts useful in variouscatalytic reactions. In some embodiments, the catalysts are bulkcatalysts (i.e., not nanowire or other nanostructured catalysts). Thebulk catalysts can be crystalline or non-crystalline and have variousparticle sizes.

In other embodiments, the catalysts are nanostructured catalysts, suchas nanowires. For example, embodiments of the catalysts are nanowireswhich are substantially straight such that the ratio of effective lengthto actual length is 1 or in some embodiments is within about 5%, 4%, 3%,2% or 1% of 1. In some embodiments, the nanowires are singlecrystalline.

In other embodiments, the catalysts are nanowires which have a bentmorphology. Embodiments of such nanowires can be characterized as havinga ratio of effective length to actual length of less than one. Incertain embodiments of the bent nanowires, the nanowires have a ratio ofeffective length to actual length of less than about 0.99, less thanabout 0.95, less than about 0.90 or even less than about 0.80. In someother embodiments, the nanowires are polycrystalline.

Certain properties of various embodiments of the catalytic nanowires aredescribed in more detail in co-pending U.S. application Ser. No.13/115,082 (U.S. Pub. No. 2012/0041246), Ser. No. 13/689,514 (U.S. Pub.No. 2013/0158322) and Ser. No. 13/689,611 (U.S. Pub. No. 2013/0165728),which applications were incorporated by reference above. Scanningelectron micrographs (SEM) of representative nanowire catalysts areprovided in FIGS. 7A and 7B.

In some embodiments, the catalysts comprise one or more metal elementsfor example, the catalysts may be mono-metallic, bi-metallic,tri-metallic, etc. (i.e., contain one, two, three, etc., metalelements). In some embodiments, the metal elements are present in thecatalysts in elemental form while in other embodiments the metalelements are present in oxidized form. In other embodiments the metalelements are present in the catalysts in the form of a compoundcomprising a metal element. The metal element or compound comprising themetal element may be in the form of oxides (e.g., mixed oxides),hydroxides, carbonates, oxy-hydroxides, oxycarbonates, salts, hydrates,and the like. The metal element or compound comprising the metal elementmay also be in the form of any of a number of different polymorphs orcrystal structures. Surprisingly, it has been found that addition ofdopants to certain metal oxides increases the catalytic activity of thecatalyst in the OCM and other reactions.

The present inventors have discovered that erbium, in combination withat least one other lanthanide element, is an effective catalyst for OCM.Accordingly, in one embodiment the heterogeneous catalysts of thepresent disclosure is a catalyst comprising a mixed oxide base material,the mixed oxide comprising erbium (Er) and at least one furtherlanthanide element.

In still other embodiments of the foregoing catalyst, the mixed oxidehas the following formula (I):

Ln_(x)Er_(y)O_(z)   (I)

wherein:

Ln is the lanthanide element;

Er is erbium;

O is oxygen; and

x, y and z are each independently numbers greater than 0.

Oxidized lanthanide metals typically exist in the +3 oxidation state,however in the case of Ce, Pr and Tb, the +4 oxidation state is alsocommon and oxides of these metals often include lanthanides in the +3and/or +4 oxidation states. Accordingly, the values for x, y and z arevariable and are limited only by the stable oxidation state of theparticular lanthanide and the molar ratio of the lanthanide in thecatalyst. For sake of simplicity, some of the specific examples herein(including those examples in Tables 1-20) illustrate lanthanide oxides,wherein the lanthanide metal(s) is in the +3 oxidation state, but it isunderstood that lanthanide oxides having lanthanides in the +4 and/or amixture of the +3 and +4 oxidation states are also included within thescope of embodiments of the invention.

Accordingly, in some embodiments x, y and z are selected such that theoverall charge of the catalyst is about 0. As used herein, “about 0”with respect to the charge of a catalyst refers to a charge state whichis either 0 (i.e., neutral) or close to 0, for example within 5%, 4%,3%, 2% or 1% of 0. In other embodiments, x, y and z are selected suchthat z is from 150% to 200% of the sum of x and y. In other embodiments,x, y and z are selected such that z is from 150% to 175% of the sum of xand y. In some other embodiments, x, y and z are selected such that z isfrom 175% to 200% of the sum of x and y. In different embodiments, x, yand z are selected such that z is about 150% of the sum of x and y. Inother different embodiments, x, y and z are selected such that z isabout 160% of the sum of x and y. In yet other embodiments, x, y and zare selected such that z is about 170% of the sum of x and y. In moreembodiments, x, y and z are selected such that z is about 180% of thesum of x and y. In other embodiments, x, y and z are selected such thatz is about 190% of the sum of x and y. In more other embodiments, x, yand z are selected such that z is about 200% of the sum of x and y. Insome embodiments, x, y and z are integers (i.e., not fractionalnumbers), for example integers selected from 1, 2, and 3. In someembodiments, x is 1, y is 1 and z is 3. In other embodiments, x is 3, yis 1, and z is 6. In more embodiments, x is 1, y is 3 and z is 6.

In various embodiments of the foregoing, the mixed oxide comprisesLnErO_(3-3.5), Ln₃ErO_(6-7.5) or LnEr₃O_(6-6.5). In various embodimentsof the foregoing, the mixed oxide comprises LnErO₃, Ln₃ErO₆ or LnEr₃O₆.In various embodiments of the foregoing, the mixed oxide comprisesLnErO₃ or Ln₃ErO₆. In some of these embodiments, Ln is La. In otherembodiments, Ln is Ce. In more embodiments, Ln is Pr. In still otherembodiments, Ln is Nd. In still more other embodiments, Ln is Sm. Inother embodiments, Ln is Eu. In more embodiments, Ln is Gd. In stillother embodiments, Ln is Tb. In still more other embodiments, Ln is Dy.In other embodiments, Ln is Ho. In more embodiments, Ln is Tm. In stillother embodiments, Ln is Yb. In still more other embodiments, Ln is Lu.

In various other embodiments, the disclosure provides a catalystcomprising a mixed oxide base material, the mixed oxide base materialcomprising two different lanthanide elements, provided that one of thelanthanide elements is not lanthanum when the other lanthanide elementis neodymium. For example, in certain embodiments the disclosure isdirected to a catalyst comprising a mixed oxide base material having thefollowing formula (II):

Ln1_(a)Ln2_(b)O_(c)   (II)

wherein:

Ln1 and Ln2 are independently different lanthanide elements;

O is oxygen; and

a, b and c are each independently numbers greater than 0; and

provided that Ln1 or Ln2 is not neodymium (Nd) when the other of Ln1 orLn2 is Lanthanum (La).

In some embodiments of the foregoing, Ln1 is Gd and Ln2 is Nd. In someembodiments, the catalyst further comprises a dopant, for example analkaline earth metal dopant such as calcium. In some embodiments, thecatalyst comprises a base material comprising a mixed oxide of Gd and Ndand a calcium dopant.

In other embodiments, a, b and c are selected such that the overallcharge of the catalyst is about 0. As used herein, “about 0” withrespect to the charge of a catalyst refers to a charge state which iseither 0 (i.e., neutral) or close to 0, for example within 5%, 4%, 3%,2% or 1% of 0. In other embodiments, a, b and c are selected such that cis from 150% to 200% of the sum of a and b. In other embodiments, a, band c are selected such that c is from 150% to 175% of the sum of a andb. In some other embodiments, a, b and c are selected such that c isfrom 175% to 200% of the sum of a and b. In different embodiments, a, band c are selected such that c is about 150% of the sum of a and b. Inother different embodiments, a, b and c are selected such that c isabout 160% of the sum of a and b. In yet other embodiments, a, b and care selected such that c is about 170% of the sum of a and b. In moreembodiments, a, b and c are selected such that c is about 180% of thesum of a and b. In other embodiments, a, b and c are selected such thatc is about 190% of the sum of a and b. In more other embodiments, a, band c are selected such that c is about 200% of the sum of a and b. Insome embodiments, a, b and c are integers, for example integers selectedfrom 1, 2, and 3. In some embodiments, a is 1, b is 1 and c is 3. Inother embodiments, a is 3, b is 1, and c is 6. In more embodiments, a is1, b is 3 and c is 6.

In different embodiments, the disclosure provides a catalyst comprisinga mixed oxide base material, the mixed oxide base material comprisingthree different lanthanide elements. For example, in some embodimentsthe catalyst comprising a mixed oxide base material has the followingformula (III):

Ln1_(a)Ln2_(b)Ln3_(d)Ln4_(e)Ln5_(f)O_(c)   (III)

wherein:

Ln1, Ln2, Ln3, Ln4 and Ln5 are independently different lanthanideelements;

O is oxygen; and

a, b, c and d are each independently numbers greater than 0; and

e and f are independently 0 or a number greater than 0.

In some embodiments of catalyst (III), a, b, c, d, e and f are selectedsuch that the overall charge of the catalyst is about 0. In otherembodiments, a, b, c, d, e and f are selected such that c is from 150%to 200% of the sum of a, b, d, e and f. In other embodiments, a, b, c,d, e and f are selected such that c is from 150% to 175% of the sum ofa, b, d, e and f. In some other embodiments, a, b, c, d, e and f areselected such that c is from 175% to 200% of the sum of a, b, d, e andf. In different embodiments, a, b, c, d, e and f are selected such thatc is about 150% of the sum of a, b, d, e and f. In other differentembodiments, a, b, c, d, e and f are selected such that c is about 160%of the sum of a, b, d, e and f. In yet other embodiments, a, b, c, d, eand f are selected such that c is about 170% of the sum of a, b, d, eand f. In more embodiments, a, b, c, d, e and f are selected such that cis about 180% of the sum of a, b, d, e and f. In other embodiments, a,b, c, d, e and f are selected such that c is about 190% of the sum of a,b, d, e and f. In more other embodiments, a, b, c, d, e and f areselected such that c is about 200% of the sum a, b, d, e and f. In someembodiments, a, b, c, d, e and f are integers, for example integersselected from 1, 2, and 3. In certain embodiments, b is 0. In otherembodiments, b is a number greater than 0.

In some embodiments of catalyst (III), a, b, c, d, e and f are selectedsuch that the overall charge of the catalyst is about 0. In certainembodiments, e is 0. In other embodiments, e is a number greater than 0.In certain embodiments, f is 0. In other embodiments, f is a numbergreater than 0.

With regard to the foregoing catalysts (II and III), the lanthanideelements can be selected from any of the lanthanide elements, providedthat Ln1, Ln2, Ln3, Ln4 and Ln5 are different. In some embodiments, Ln1is La. In other embodiments, Ln1 is Ce. In more embodiments, Ln1 is Pr.In still other embodiments, Ln1 is Nd. In still more other embodiments,Ln1 is Sm. In other embodiments, Ln1 is Eu. In more embodiments, Ln1 isGd. In still other embodiments, Ln1 is Tb. In still more otherembodiments, Ln1 is Dy. In other embodiments, Ln1 is Ho. In otherembodiments, Ln1 is Er. In more embodiments, Ln1 is Tm. In still otherembodiments, Ln1 is Yb. In still more other embodiments, Ln1 is Lu.

In further embodiments, of the foregoing, Ln1 is selected according tothe immediately foregoing paragraph and Ln2 is selected from a differentlanthanide. For example, in some embodiments, Ln2 is La. In otherembodiments, Ln2 is Ce. In more embodiments, Ln2 is Pr. In still otherembodiments, Ln2 is Nd. In still more other embodiments, Ln2 is Sm. Inother embodiments, Ln2 is Eu. In more embodiments, Ln2 is Gd. In stillother embodiments, Ln2 is Tb. In still more other embodiments, Ln2 isDy. In other embodiments, Ln2 is Ho. In other embodiments, Ln2 is Er. Inmore embodiments, Ln2 is Tm. In still other embodiments, Ln2 is Yb. Instill more other embodiments, Ln2 is Lu.

In various embodiments, Ln1 is La and Ln2 is Nd. For example, in someembodiments, the catalyst comprises La₃NdO₆.

In other embodiments, Ln1 and Ln2 are selected as above and, Ln3 is La.In other embodiments, Ln3 is Ce. In more embodiments, Ln3 is Pr. Instill other embodiments, Ln3 is Nd. In still more other embodiments, Ln3is Sm. In other embodiments, Ln3 is Eu. In more embodiments, Ln3 is Gd.In still other embodiments, Ln3 is Tb. In still more other embodiments,Ln3 is Dy. In other embodiments, Ln3 is Ho. In other embodiments, Ln3 isEr. In more embodiments, Ln3 is Tm. In still other embodiments, Ln3 isYb. In still more other embodiments, Ln3 is Lu.

In other embodiments, Ln1, Ln2 and Ln3 are selected as above and, Ln4 isLa. In other embodiments, Ln4 is Ce. In more embodiments, Ln4 is Pr. Instill other embodiments, Ln4 is Nd. In still more other embodiments, Ln4is Sm. In other embodiments, Ln4 is Eu. In more embodiments, Ln4 is Gd.In still other embodiments, Ln4 is Tb. In still more other embodiments,Ln4 is Dy. In other embodiments, Ln4 is Ho. In other embodiments, Ln4 isEr. In more embodiments, Ln4 is Tm. In still other embodiments, Ln4 isYb. In still more other embodiments, Ln4 is Lu.

In other embodiments, Ln1, Ln2, Ln3 and Ln4 are selected as above and,Ln5 is La. In other embodiments, Ln5 is Ce. In more embodiments, Ln5 isPr. In still other embodiments, Ln5 is Nd. In still more otherembodiments, Ln5 is Sm. In other embodiments, Ln5 is Eu. In moreembodiments, Ln5 is Gd. In still other embodiments, Ln5 is Tb. In stillmore other embodiments, Ln5 is Dy. In other embodiments, Ln5 is Ho. Inother embodiments, Ln5 is Er. In more embodiments, Ln5 is Tm. In stillother embodiments, Ln5 is Yb. In still more other embodiments, Ln5 isLu.

Further, and in addition to the foregoing proviso with respect tocatalyst (II), in some other embodiments Ln1 or Ln2 is not Ce when theother of Ln1 or Ln2 is La. In other embodiments, Ln1 or Ln2 is not Prwhen the other of Ln1 or Ln2 is La. In other embodiments, Ln1 or Ln2 isnot Pm when the other of Ln1 or Ln2 is La. In other embodiments, Ln1 orLn2 is not Sm when the other of Ln1 or Ln2 is La. In other embodiments,Ln1 or Ln2 is not Eu when the other of Ln1 or Ln2 is La. In otherembodiments, Ln1 or Ln2 is not Gd when the other of Ln1 or Ln2 is La. Inother embodiments, Ln1 or Ln2 is not Tb when the other of Ln1 or Ln2 isLa. In other embodiments, Ln1 or Ln2 is not Dy when the other of Ln1 orLn2 is La. In other embodiments, Ln1 or Ln2 is not Ho when the other ofLn1 or Ln2 is La. In other embodiments, Ln1 or Ln2 is not Er when theother of Ln1 or Ln2 is La. In other embodiments, Ln1 or Ln2 is not Tmwhen the other of Ln1 or Ln2 is La. In other embodiments, Ln1 or Ln2 isnot Yb when the other of Ln1 or Ln2 is La. In other embodiments, Ln1 orLn2 is not Lu when the other of Ln1 or Ln2 is La.

In other embodiments of catalyst (III), none of Ln1, Ln2 or Ln3 is Ndwhen one other of Ln1, Ln2 or Ln3 is La. In still other embodiments ofcatalyst (III), none of Ln1, Ln2, Ln3, Ln4 or Ln5 is Nd when one otherof Ln1, Ln2, Ln3, Ln4 or Ln5 is La.

In different embodiments of the foregoing catalysts, the mixed oxidecomprises various different forms of oxidized metals (e.g., twodifferent lanthanides, such as erbium and one or more other lanthanide).For example, in some embodiments the mixed oxide base material comprisesdifferent forms of oxidized metals selected from an oxide, hydroxide,oxy-hydroxide, carbonate, oxy-carbonate, hydroxy carbonate oroxy-hydroxy-carbonate and combinations thereof.

The mixed oxide base material may also be in different forms in variousdifferent embodiments, for example in one embodiment the mixed oxidecomprises a physical blend of two different lanthanide elements, such asa blend of erbium and another lanthanide.

In various embodiments of any of the foregoing catalysts, the catalystis a bulk catalyst. In other embodiments, the catalysts arenanostructured catalysts, such as nanowires. For example, embodiments ofthe catalysts are nanowires which are substantially straight such thatthe ratio of effective length to actual length is 1 or in someembodiments is within about 5%, 4%, 3%, 2% or 1% of 1. In someembodiments, the nanowires are single crystalline.

In other embodiments, the catalysts are nanowires which have a bentmorphology. Embodiments of such nanowires can be characterized as havinga ratio of effective length to actual length of less than one. Incertain embodiments of the bent nanowires, the nanowires have a ratio ofeffective length to actual length of less than about 0.99, less thanabout 0.95, less than about 0.90 or even less than about 0.80. In someother embodiments, the nanowires are polycrystalline.

Although not required for catalytic activity, various embodiments of theforgoing catalysts further comprise one or more doping element. Theoptional doping elements are selected from any element of the periodictable and are present in concentrations effective to obtain the desiredresult.

Typically, doping elements are added to a catalyst base material toincrease the catalytic activity (e.g., yield, selectivity, conversion,etc.) of the catalyst with respect to a certain reaction, although ifdesired a doping element which decreases catalytic activity (a poison)may also be added. Accordingly, in one embodiment the catalysts comprisea doping element which is a promoter, for example in one embodiment thedoping element is a promoter with respect to the oxidative coupling ofmethane (i.e., increases the catalytic activity of the base materialwith respect to the oxidative coupling of methane.

In some embodiments the optional doping element is selected from one ormore groups of the periodic table. In some embodiments, the dopingelement is a lanthanide element. In one embodiment, the catalystcomprises a doping element selected from an element in group 1 of theperiodic table. In other embodiments, the catalyst comprises a dopingelement selected from an element in group 2 of the periodic table. Indifferent embodiments, the catalyst comprises a doping element selectedfrom an element in group 3 of the periodic table. In some otherembodiments, the catalyst comprises a doping element selected from anelement in group 4 of the periodic table. In still more embodiments, thecatalyst comprises a doping element selected from an element in group 5of the periodic table. In yet other embodiments, the catalyst comprisesa doping element selected from an element in group 6 of the periodictable.

In another embodiment, the catalyst comprises a doping element selectedfrom an element in group 7 of the periodic table. In other embodiments,the catalyst comprises a doping element selected from an element ingroup 8 of the periodic table. In different embodiments, the catalystcomprises a doping element selected from an element in group 9 of theperiodic table. In some other embodiments, the catalyst comprises adoping element selected from an element in group 10 of the periodictable. In still more embodiments, the catalyst comprises a dopingelement selected from an element in group 11 of the periodic table. Inyet other embodiments, the catalyst comprises a doping element selectedfrom an element in group 12 of the periodic table.

In still other different embodiments, the catalyst comprises a dopingelement selected from an element in group 13 of the periodic table. Inother embodiments, the catalyst comprises a doping element selected froman element in group 14 of the periodic table. In different embodiments,the catalyst comprises a doping element selected from an element ingroup 15 of the periodic table. In some other embodiments, the catalystcomprises a doping element selected from an element in group 16 of theperiodic table. In still more embodiments, the catalyst comprises adoping element selected from an element in group 17 of the periodictable.

Combinations of different doping elements from different groups of theperiodic table are also included in various other embodiments. Forexample, in some embodiments the catalysts comprise two or more dopingelements selected from groups 2 and 4, groups 6 and 13, groups 4 and 13,groups 2 and 6, groups 2 and 13 or groups 4 and 6. In other embodiments,the catalysts comprise one or more doping element selected from groups1, 2, 3, 4, 6 and 13 of the periodic table. In still other embodiments,the catalysts comprise one or more doping element selected from groups2, 4, 6 and 13 of the periodic table.

In still other embodiments, the catalyst comprises at least one dopantfrom any of groups 1-17 and second dopant selected from any one ofgroups 1-17. In certain embodiments, the second doping element isselected from groups 1, 2, 3, 4, 6, 13 and the lanthanides. In someembodiments, the second doping element is selected from an element ingroup 1 of the periodic table. In other embodiments, the second dopingelement is selected from an element in group 2 of the periodic table. Inmore embodiments, the second doping element is selected from an elementin group 3 of the periodic table. In still other embodiments, the seconddoping element is selected from an element in group 4 of the periodictable. In yet more embodiments, the second doping element is selectedfrom an element in group 6 of the periodic table. In still otherembodiments, the second doping element is selected from an element ingroup 13 of the periodic table. In more other embodiments, the seconddoping element is selected from a lanthanide element.

In still other embodiments, the catalyst comprises at least two dopingelements, wherein the first doping element is selected as describedabove and the second doping element is selected from Ce, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, Lu, B, Ba, Sr, Mg, Ca, K, W, Hf, Ga, Y and Al. Insome embodiments, the second doping element is Ce. In other embodiments,the second doping element is Sm. In more embodiments, the second dopingelement is Eu. In yet more embodiments, the second doping element is Gd.In some embodiments, the second doping element is Tb. In otherembodiments, the second doping element is Dy. In more embodiments, thesecond doping element is Ho. In yet more embodiments, the second dopingelement is Er. In some embodiments, the second doping element is Tm. Inother embodiments, the second doping element is Yb. In more embodiments,the second doping element is Lu. In yet more embodiments, the seconddoping element is B. In some embodiments, the second doping element isBa. In other embodiments, the second doping element is Sr. In moreembodiments, the second doping element is Mg. In yet more embodiments,the second doping element is Ca. In some embodiments, the second dopingelement is K. In other embodiments, the second doping element is W. Inmore embodiments, the second doping element is Hf. In yet moreembodiments, the second doping element is Ga. In some embodiments, thesecond doping element is Y. In other embodiments, the second dopingelement is Al.

In some embodiments, the doping element is selected from Mg, Ca, Sr andBa. In other embodiments, the doping element is selected from Sr and Ba.In yet other embodiments, the doping element is Zr or Hf. In variousembodiments of the foregoing, the catalyst comprises a doping elementselected from Mg, Ca, Sr, Ba, Zr and Hf and a second doping elementselected from groups 1, 2 and the lanthanides. For example in someembodiments, the second doping is Sr, K, Ba, Na, Eu or Tm. In someembodiments the second doping element is Sr. In other embodiments, thesecond doping element is K. In some embodiments the second dopingelement is Ba. In other embodiments, the second doping element is Na. Insome embodiments the second doping element is Eu. In other embodiments,the second doping element is Tm.

In some embodiments, the doping element is selected from an element ingroup 6, such as W. In various further embodiments, such catalystsfurther comprise a doping element selected from the lanthanides, such asEr. In this regard the Er is considered a doping element and is presentin addition to the Er already present in the catalyst.

In still other embodiments, the catalysts comprise a doping elementselected from group 13 of the periodic table, for example B, Al or Ga.In some embodiments, the doping element is B. In some other embodiments,the doping element is Al. In some more embodiments, the doping elementis Ga. In further embodiments of the foregoing, the catalyst furthercomprises a doping element from group 2 of the periodic table, forexample Sr, Ba, Ca or Mg. In some embodiments, this further dopingelement is Sr. In other embodiments, the further doping element is Ba.In other embodiments, the further doping element is Ca. In otherembodiments, the further doping element is Mg.

In some embodiments, the doping element is selected from one or moreelements in groups 2, 6 and 13. For example, in some embodiments theelement is selected from Sr, Ba, W and B. In some embodiments, theelement is Sr. In some embodiments, the element is Ba. In someembodiments, the element is W. In some embodiments, the element is B.

Combinations of Sr, Ba, W and B as doping elements are also within thescope of certain embodiments of the invention. For example, in additionto the base catalyst, some embodiments comprise doping combinationsselected from Sr/Ba, Sr/W and Sr/B. In other embodiments, the dopingcombination is selected from Ba/Sr, Ba/W and Ba/B. In other embodiments,the dopants comprise W/Sr. W/Ba or W/B. In still other embodiments, thedopants comprise B/Sr, B/Ba or B/W.

In still more embodiments, the doping elements comprise one of thefollowing combinations: Sr/Ba/W, Sr/Ba/B, Sr/W/B or Ba/W/B. In someembodiments, the dopant combination comprises Sr/Ba/W/B.

In other embodiments, the catalyst comprises one of the following dopingcombinations: W, Sr, Ba, B, Sr/Ce, Sr/Sm, Sr/Eu, Sr/Gd, Sr/Tb, Sr/Dy,Sr/Er, Sr/Tm, Sr/Tb, Sr/Lu, Sr/Ba/B, Sr/B, Ba/B, Ba/Sr, Er/W, Sr/K,Ba/Ce, Ca/W, Sr/Hf, Sr/Hf/K, Ba/Hf, Ga/Mg, Sr/Ca, Y/Ba, Sr/Ga/Mg, Sr/Y,Na/Zr/Eu/Tm, Sr/B/Y, Ca/B, Sr/Ga, Sr/Al, Sr/W, Ba/W, B/W, Sr/Ba/W,Sr/W/B, Ba/W/B or Sr/Ba/W/B.

The doping elements, when present, in the foregoing mixed oxides isselected from any of groups 1-17, and in some embodiments the dopingelement is selected according to any of the foregoing describedembodiments.

In various other embodiments, the disclosure provides a catalystcomprising a base material comprising an oxide of one or more lanthanideelements and a dopant combination selected from Sr/Sm, Sr/Gd, Sr/Dy,Sr/Er, Sr/Lu, Sr/Ba/B, Ba/B, Ba/Sr, Er/W, Sr/K, Ba/Ce, Ba/Hf, Ga/Mg,Mg/Er, Y/Ba, Sr/Ga/Mg, Sr/Y, Sr/B/Y, Ca/B, Sr/Al, Ba/W, B/W, Sr/Ba/W,Sr/W/B, Ba/W/B and Sr/Ba/W/B.

In various embodiments, the foregoing oxide has the following formula(III):

Ln1_(a)Ln2_(b)Ln3_(d)Ln4_(e)Ln5_(f)O_(c)   (III)

wherein:

Ln1, Ln2, Ln3, Ln4 and Ln5 are independently different lanthanideelements;

O is oxygen; and

a and c are each independently numbers greater than 0; and

b, d, e and f are independently 0 or a number greater than 0.

In various embodiments of the foregoing catalyst (III), Ln1, Ln2, Ln3,Ln4 and Ln5 are selected according to the foregoing description withrespect to catalyst (III). Further embodiments, include embodimentswherein a, b, c, d, e and f are selected according to the foregoingdescription with respect to catalyst (III).

In some embodiments, the dopant combination consists essentially ofSr/Sm, Sr/Gd, Sr/Dy, Sr/Er, Sr/Lu, Sr/Ba/B, Ba/B, Ba/Sr, Er/W, Sr/K,Ba/Ce, Ba/Hf, Ga/Mg, Mg/Er, Y/Ba, Sr/Ga/Mg, Sr/Y, Sr/B/Y, Ca/B, Sr/Al,Ba/W, B/W, Sr/Ba/W, Sr/W/B, Ba/W/B or Sr/Ba/W/B. In other embodiments,the dopant combination consists of Sr/Sm, Sr/Gd, Sr/Dy, Sr/Er, Sr/Lu,Sr/Ba/B, Ba/B, Ba/Sr, Er/W, Sr/K, Ba/Ce, Ba/Hf, Ga/Mg, Mg/Er, Y/Ba,Sr/Ga/Mg, Sr/Y, Sr/B/Y, Ca/B, Sr/Al, Ba/W, B/W, Sr/Ba/W, Sr/W/B, Ba/W/Bor Sr/Ba/W/B. In some embodiments, the foregoing catalyst (III) is abulk catalyst and in other embodiments the foregoing catalyst (III) is ananowire catalyst.

In other embodiments, the present disclosure provides a bulk catalystcomprising a base material comprising an oxide of one or more lanthanideelements and a dopant combination selected from Sr/Ce, Sr/Tb, Sr/B andSr/Hf/K.

In some embodiments, the bulk catalyst oxide has the following formula(III):

Ln1_(a)Ln2_(b)Ln3_(d)Ln4_(e)Ln5_(f)O_(c)   (III)

wherein:

Ln1, Ln2, Ln3, Ln4 and Ln5 are independently different lanthanideelements;

O is oxygen; and

a and c are each independently numbers greater than 0; and

b, d, e, and f are independently 0 or a number greater than 0.

In various embodiments of the foregoing bulk catalyst (III), Ln1, Ln2,Ln3, Ln4 and Ln5 are selected according to the foregoing descriptionwith respect to catalyst (III). Further embodiments, include embodimentswherein a, b, c, d, e and f are selected according to the foregoingdescription with respect to catalyst (III).

In other the dopant combination consists essentially of Sr/Ce, Sr/Tb,Sr/B or Sr/Hf/K. In still more embodiments, the dopant combinationconsists of Sr/Ce, Sr/Tb, Sr/B or Sr/Hf/K.

It should be noted that the foregoing catalyst formulas (I, II and III)refer to the base catalyst formula and do not include dopants. Forexample, the lanthanide elements (i.e., Ln, Ln1, Ln2, Ln3, Ln4 or Ln5)illustrated as part of the foregoing catalysts are part of the basecatalyst and not a dopant. Instead, dopants are an optional feature inaddition to the base catalyst material. Dopants are generally, but notalways, present in lower quantities than the elements in the basematerial.

In other embodiments is provided a catalyst comprising a mixture of aGroup 3 element and a Group 4 element or lanthanide element, thecatalyst further comprising an alkaline earth metal dopant. In some ofthe embodiments, the catalyst comprises one of the following mixtures ofelements: Y/Zr, Y/Ti, Y/Gd, Y/Ce, Y/La, Y/Ca, Y/Ti, Y/Eu. In variousembodiments, the alkaline earth metal dopant is barium, strontium orcalcium.

In some embodiments, the catalyst comprises Ca/Sr/Y/Zr. In some otherembodiments, the catalyst comprises Nd/Ca/Sr/Y/Zr. In some differentembodiments, the catalyst comprises Ca/Y/Ti. In yet other embodiments,the catalyst comprises Ba/Gd/Y. In more embodiments, the catalystcomprises Ba/Ce/Y. In some other embodiments, the catalyst comprisesBa/La/Y. In other embodiments, the catalyst comprises Ba/Ca/Y. In someembodiments, the catalyst comprises Ba/Y/Ti. In yet other differentembodiments, the catalyst comprises Ba/Eu/Y.

In still other embodiments, a catalyst comprising a Group 4 orlanthanide oxide in combination with an alkaline earth metal dopant isprovided. In some of these embodiments, the dopant is barium orstrontium. In some specific embodiments, the catalyst comprises Ba/HfO₃.In some other embodiments, the catalyst comprises Sr/HfO₃. In moreembodiments, the catalyst comprises Ba/CeO₃. In still other embodiments,the catalyst comprises Ba/TiO₃. In some other embodiments, the catalystcomprises Ba/W/Nd₂O₃. In some different embodiments, the catalystcomprises Ba/W/Er₂O₃.

In certain embodiments of any of the foregoing catalysts, the catalystscomprises a C₂+ selectivity of greater than 50% and a methane conversionof greater than 20% when the catalyst is employed as a heterogeneouscatalyst in the oxidative coupling of methane at a temperature of 750°C. or less.

In other embodiments, the C₂+ selectivity of the catalysts is greaterthan 60% when the catalyst is employed as a heterogeneous catalyst inthe oxidative coupling of methane at a temperature of 750° C. or less.

In other embodiments, the catalysts have a C2+ yield greater than 10%,or even greater than 15% when the catalyst is employed as aheterogeneous catalyst in the oxidative coupling of methane at atemperature of 750° C. or less.

In some other embodiments, the catalysts comprise a methane conversiongreater than 20% or greater than 30% when the catalyst is employed as aheterogeneous catalyst in the oxidative coupling of methane at atemperature of 750° C. or less.

In other certain embodiments, the catalysts are capable of methaneconversions in an OCM reaction of greater than 20% and C₂+ selectivitiesof greater than 50% at temperatures ranging from about 550 C to about750 C, for example, from about 600 C to about 700 C. In otherembodiments of the foregoing, the methane conversion is greater than22%, greater than 24% or even greater than 26%. In still otherembodiments of any of the foregoing, the C2+ selectivity of thecatalysts is greater than 55% or even greater than 60%.

In various embodiments, of any of the above catalysts, the catalystcomprises a C2+ selectivity of greater than 50% and a methane conversionof greater than 20% when the catalyst is employed as a heterogeneouscatalyst in the oxidative coupling of methane at a temperature of 750°C. or less, 700° C. or less, 650° C. or less or even 600° C. or less.

In more embodiments, of any of the above catalysts, the catalystcomprises a C2+ selectivity of greater than 50%, greater than 55%,greater than 60%, greater than 65%, greater than 70%, or even greaterthan 75%, and a methane conversion of greater than 20% when the catalystis employed as a heterogeneous catalyst in the oxidative coupling ofmethane at a temperature of 750° C. or less.

In other embodiments, of any of the above catalysts, the catalystcomprises a C2+ selectivity of greater than 50%, and a methaneconversion of greater than 20%, greater than 25%, greater than 30%,greater than 35%, greater than 40%, greater than 45%, or even greaterthan 50% when the catalyst is employed as a heterogeneous catalyst inthe oxidative coupling of methane at a temperature of 750° C. or less.In some embodiments of the foregoing, the methane conversion and C2+selectivity are calculated based on a single pass basis (i.e., thepercent of methane converted or C2+ selectivity upon a single pass overthe catalyst or catalytic bed, etc.)

In various embodiments, the foregoing performance parameters of thecatalysts (e.g., conversion, yield, selectivity) are determined when theoxidative coupling of methane is performed at a temperature of 700° C.or less. In other embodiments, the parameters are determined when theoxidative coupling of methane is performed at reaction inlet pressuresranging from 1 atm to 16 atm.

In various embodiments of the foregoing, the methane conversion, C₂+selectivity, or C2+ yield, or combinations thereof, are measured in a 4millimeter inner diameter tube with a methane to oxygen ratio of 5.5:1using air as an oxidant, wherein the temperature is 650° C.

In various other embodiments, the oxidative coupling of methane isperformed at a temperature of 700° C. or less, and in some differentembodiments, the oxidative coupling of methane is performed at reactioninlet pressures ranging from 1 atm to 16 atm.

The metal oxides disclosed herein can be in the form of oxides,oxyhydroxides, hydroxides, oxycarbonates or combination thereof afterbeing exposed to moisture, carbon dioxide, undergoing incompletecalcination or combination thereof.

The foregoing catalysts comprise 0, 1, 2, 3, 4 or more doping elements.In this regard, each dopant may be present in the catalysts (for exampleany of the catalysts described above and/or disclosed in Tables 1-20) inup to 75% by weight of the catalyst. For example, in one embodiment theconcentration of a first doping element (when present) ranges from 0.01%to 1% w/w, 1%-5% w/w, 5%-10% w/w. 10%-20% w/w, 20%-30% w/w, 30%-40% w/wor 40%-50% w/w, for example about 1% w/w, about 2% w/w, about 3% w/w,about 4% w/w, about 5% w/w, about 6% w/w, about 7% w/w, about 8% w/w,about 9% w/w, about 10% w/w, about 11% w/w, about 12% w/w, about 13%w/w, about 14% w/w, about 15% w/w, about 16% w/w, about 17% w/w, about18% w/w, about 19% w/w or about 20% w/w.

In other embodiments, the concentration of a second doping element (whenpresent) ranges from 0.01% to 1% w/w, 1%-5% w/w, 5%-10% w/w. 10%-20%w/w, 20%-30% w/w, 30%-40% w/w or 40%-50% w/w, for example about 1% w/w,about 2% w/w, about 3% w/w, about 4% w/w, about 5% w/w, about 6% w/w,about 7% w/w, about 8% w/w, about 9% w/w, about 10% w/w, about 11% w/w,about 12% w/w, about 13% w/w, about 14% w/w, about 15% w/w, about 16%w/w, about 17% w/w, about 18% w/w, about 19% w/w or about 20% w/w.

In other embodiments, the concentration of a third doping element (whenpresent) ranges from 0.01% to 1% w/w, 1%-5% w/w, 5%-10% w/w. 10%-20%w/w, 20%-30% w/w, 30%-40% w/w or 40%-50% w/w, for example about 1% w/w,about 2% w/w, about 3% w/w, about 4% w/w, about 5% w/w, about 6% w/w,about 7% w/w, about 8% w/w, about 9% w/w, about 10% w/w, about 11% w/w,about 12% w/w, about 13% w/w, about 14% w/w, about 15% w/w, about 16%w/w, about 17% w/w, about 18% w/w, about 19% w/w or about 20% w/w.

In other embodiments, the concentration of a fourth doping element (whenpresent) ranges from 0.01% to 1% w/w, 1%-5% w/w, 5%-10% w/w. 10%-20%w/w, 20%-30% w/w, 30%-40% w/w or 40%-50% w/w, for example about 1% w/w,about 2% w/w, about 3% w/w, about 4% w/w, about 5% w/w, about 6% w/w,about 7% w/w, about 8% w/w, about 9% w/w, about 10% w/w, about 11% w/w,about 12% w/w, about 13% w/w. about 14% w/w, about 15% w/w, about 16%w/w, about 17% w/w, about 18% w/w, about 19% w/w or about 20% w/w.

In other embodiments, the concentration of the dopant is measured interms of atomic percent (at/at). In some of these embodiments, eachdopant may be present in the catalysts (for example any of the catalystsdescribed above and/or disclosed in Tables 1-20) in up to 75% at/at. Forexample, in one embodiment the concentration of a first doping element(when present) ranges from 0.01% to 1% at/at, 1%-5% at/at, 5%-10% at/at.10%-20% at/at, 20%-30% at/at, 30%-40% at/at or 40%-50% at/at, forexample about 1% at/at, about 2% at/at, about 3% at/at, about 4% at/at,about 5% at/at, about 6% at/at, about 7% at/at, about 8% at/at, about 9%at/at, about 10% at/at, about 11% at/at, about 12% at/at, about 13%at/at, about 14% at/at, about 15% at/at, about 16% at/at, about 17%at/at, about 18% at/at, about 19% at/at or about 20% at/at.

In other embodiments, the concentration of a second doping element (whenpresent) ranges from 0.01% to 1% at/at, 1%-5% at/at, 5%-10% at/at.10%-20% w/w, 20%-30% at/at, 30%-40% at/at or 40%-50% at/at, for exampleabout 1 at/at, about 2% at/at, about 3% at/at, about 4% at/at, about 5%at/at, about 6% at/at, about 7% at/at, about 8% at/at, about 9% at/at,about 10% at/at, about 11% at/at, about 12% at/at, about 13% at/at,about 14% at/at, about 15% at/at, about 16% at/at, about 17% at/at,about 18% at/at, about 19% at/at or about 20% at/at.

In other embodiments, the concentration of a third doping element (whenpresent) ranges from 0.01% to 1% at/at, 1%-5% at/at, 5%-10% at/at.10%-20% w/w, 20%-30% at/at, 30%-40% at/at or 40%-50% at/at, for exampleabout 1 at/at, about 2% at/at, about 3% at/at, about 4% at/at, about 5%at/at, about 6% at/at, about 7% at/at, about 8% at/at, about 9% at/at,about 10% at/at, about 11 at/at, about 12% at/at, about 13% at/at, about14% at/at, about 15% at/at, about 16% at/at, about 17% at/at, about 18%at/at, about 19% at/at or about 20% at/at.

In other embodiments, the concentration of a fourth doping element (whenpresent) ranges from 0.01% to 1% at/at, 1%-5% at/at, 5%-10% at/at.10%-20% w/w, 20%-30% at/at, 30%-40% at/at or 40%-50% at/at, for exampleabout 1 at/at, about 2% at/at, about 3% at/at, about 4% at/at, about 5%at/at, about 6% at/at, about 7% at/at, about 8% at/at, about 9% at/at,about 10% at/at, about 11 at/at, about 12% at/at, about 13% at/at, about14% at/at, about 15% at/at, about 16% at/at, about 17% at/at, about 18%at/at, about 19% at/at or about 20% at/at.

Accordingly, any of the doped catalysts described above or in Tables1-20, may comprise any of the foregoing doping concentrations.

Furthermore, different catalytic characteristics of the above dopedcatalysts can be varied or “tuned” based on the method used to preparethem. Such methods are described in more detail herein and other methodsare known in the art. In addition, the above dopants may be incorporatedeither before or after (or combinations thereof) an optional calcinationstep as described herein.

Tables 1-20 below show exemplary doped catalysts in accordance withvarious specific embodiments. Dopants are shown in the horizontal rowsand base catalyst in the vertical columns in tables 1-8. Dopants areshown in the vertical columns and base catalyst in the horizontal rowsin table 9-20. The resulting doped catalysts are shown in theintersecting cells. The variables a, b, c, x, y and z in Tables 1-20 areas defined above herein.

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The catalysts of the disclosure may be analyzed by inductively coupledplasma mass spectrometry (ICP-MS) to determine the element content ofthe catalysts. ICP-MS is a type of mass spectrometry that is highlysensitive and capable of the determination of a range of metals andseveral non-metals at concentrations below one part in 10¹². ICP isbased on coupling together an inductively coupled plasma as a method ofproducing ions (ionization) with a mass spectrometer as a method ofseparating and detecting the ions. ICP-MS methods are well known in theart.

As used throughout the specification, a catalyst composition representedby E¹/E²/E³, etc., wherein E¹, E² and E³ are each independently anelement or a compound comprising one or more elements, refers to acatalyst comprised of a mixture of E¹, E² and E³. E¹, E² and E³, etc.,are not necessarily present in equal amounts and need not form a bondwith one another. For example, a catalyst comprising Li/MgO refers to acatalyst comprising Li and MgO, for example, Li/MgO may refer to MgOdoped with Li. By way of another example, a catalyst comprisingNa/Mn/W/O refers to a catalyst comprised of a mixture of sodium,manganese, tungsten and oxygen. Generally the oxygen is in the form of ametal oxide.

In some embodiments, dopants are present in the catalysts in, forexample, less than 50 at %, less than 25 at %, less than 10 at %, lessthan 5 at % or less than 1 at %.

In other embodiments of the catalysts, the weight ratio (w/w) of thecatalyst base material to the doping element(s) ranges from 1:1 to10,000:1, 1:1 to 1,000:1 or 1:1 to 500:1.

2. Catalytic Materials

The present disclosure includes a catalytic material comprising aplurality of catalysts. In certain embodiments, the catalytic materialcomprises a support or carrier. Supports and carriers useful in thecontext of the invention are not limited and include supports andcarriers described herein as well as those known in the art, for exampleas described in U.S. application Ser. No. 13/115,082 (U.S. Pub. No.2012/0041246), Ser. No. 13/479,767 (U.S. Pat. No. 8,921,256), Ser. No.13/689,514 (U.S. Pub. No. 2013/0158322), Ser. No. 13/689,611 (U.S. Pub.No. 2013/0165728) and Ser. No. 13/901,319 (corresponding to PCT Pub. No.WO 2013/177461), and PCT App. No. US 2014/028040, the full disclosuresof which are hereby incorporated by reference in their entireties.

The support is preferably porous and has a high surface area. In someembodiments the support is active (i.e., has catalytic activity). Inother embodiments, the support is inactive (i.e., non-catalytic). Insome embodiments, the support comprises an inorganic oxide, Al₂O₃, SiO₂,TiO₂, MgO, CaO, SrO, ZrO₂, ZnO, LiAlO₂, MgAl₂O₄, MnO, MnO₂, Mn₃O₄,La₂O₃, AlPO₄, SiO₂/Al₂O₃, activated carbon, silica gel, zeolites,activated clays, activated Al₂O₃, SiC, diatomaceous earth, magnesia,aluminosilicates, calcium aluminate, support nanowires or combinationsthereof. In some embodiments the support comprises silicon, for exampleSiO₂. In other embodiments the support comprises magnesium, for exampleMgO. In yet other embodiments, the support comprises yttrium, forexample Y₂O₃. In other embodiments the support comprises zirconium, forexample ZrO₂. In yet other embodiments, the support comprises lanthanum,for example La₂O₃. In yet other embodiments, the support compriseslanthanum, for example La₂O₃. In yet other embodiments, the supportcomprises hafnium, for example HfO₂. In yet other embodiments, thesupport comprises aluminum, for example Al₂O₃. In yet other embodiments,the support comprises gallium, for example Ga₂O₃.

In still other embodiments, the support material comprises an inorganicoxide, Al₂O₃, SiO₂, TiO₂, MgO, ZrO₂, HfO₂, CaO, SrO, ZnO, LiAlO₂,MgAl₂O₄, MnO, MnO₂, Mn₂O₄, Mn₃O₄, La₂O₃, AlPO₄, activated carbon, silicagel, zeolites, activated clays, activated Al₂O₃, diatomaceous earth,magnesia, aluminosilicates, calcium aluminate, support nanowires orcombinations thereof. In yet other embodiments, a catalyst may serve asa support for another catalyst. For example, a catalyst may be comprisedof catalytic support material and adhered to or incorporated within thesupport is another catalyst. For example, in some embodiments, thecatalytic support may comprise SiO₂, MgO, TiO₂, ZrO₂, Al₂O₃, ZnO orcombinations thereof.

In still other embodiments, the support material comprises a carbonate.For example, in some embodiments the support material comprises MgCO₃,CaCO₃, SrCO₃, BaCO₃, Y₂(CO₃)₃, La₂(CO₃)₃ or combinations thereof.

In other embodiments, the support material is selected from AlPO₄,Al₂O₃, SiO₂—Al₂O₃, CaO, TiO₂, ZrO₂, MgO, SiO₂, HfO₂, In₂O₃, SiC andcombinations thereof.

In yet other embodiments, a nanowire may serve as a support for anotherbulk or nanowire catalyst. For example, a nanowire may be comprised ofnon-catalytic metal elements and adhered to or incorporated within thesupport nanowire is a catalyst as described herein. For example, in someembodiments, the support nanowires are comprised of SiO₂, MgO, CaO, SrO,TiO₂, ZrO₂, Al₂O₃, ZnO, MgCO₃, CaCO₃, SrCO₃ or combinations thereof. Theoptimum amount of catalyst present on the support depends, inter alia,on the catalytic activity of the catalyst. In some embodiments, theamount of catalyst present on the support ranges from 1 to 100 parts byweight of catalyst per 100 parts by weight of support or from 10 to 50parts by weight of catalyst per 100 parts by weight of support. In otherembodiments, the amount of catalyst present on the support ranges from100-200 parts of catalyst per 100 parts by weight of support, or 200-500parts of catalyst per 100 parts by weight of support, or 500-1000 partsof catalyst per 100 parts by weight of support. Typically, heterogeneouscatalysts are used either in their pure form or blended with inertmaterials, such as silica, alumina, etc. The blending with inertmaterials is used in order to reduce and/or control large temperaturenon-uniformities within the reactor bed often observed in the case ofstrongly exothermic (or endothermic) reactions. In the case of complexmultistep reactions, such as the reaction to convert methane intoethylene (OCM), typical blending materials can selectively slow down orquench one or more of the reactions of the system and promote unwantedside reactions. For example, in the case of the oxidative coupling ofmethane, silica and alumina can quench the methyl radicals and thusprevent the formation of ethane. In certain aspects, the presentdisclosure provides a catalytic material which solves these problemstypically associated with catalyst support material. Accordingly, incertain embodiments the catalytic activity of the catalytic material canbe tuned by blending two or more catalysts and/or catalyst supportmaterials. The blended catalytic material may comprise a catalyst asdescribed herein in combination with another catalytic material, forexample an additional bulk catalyst or a catalytic nanowire as describedin PCT Pub. Nos. WO 2011/14996; WO 2013/082318 and WO 2012/162526 whichare hereby incorporated by reference in their entireties, and/or inertsupport material.

In some embodiments, the blended catalytic materials comprise metaloxides, hydroxides, oxy-hydroxides, carbonates, oxalates of the groups1-16, lanthanides, actinides or combinations thereof. For example, theblended catalytic materials may comprise a plurality of catalysts, asdisclosed herein, and any one or more of straight nanowires,nanoparticles, bulk materials and inert support materials. The blendedcatalytic materials may be undoped or may be doped with any of thedopants described herein or other dopants useful for obtaining thedesired catalytic activity.

In one embodiment, the catalyst blend comprises at least one type 1component and at least one type 2 component. Type 1 components comprisecatalysts having a high OCM activity at moderately low temperatures andtype 2 components comprise catalysts having limited or no OCM activityat these moderately low temperatures, but are OCM active at highertemperatures. For example, in some embodiments the type 1 component is acatalyst having high OCM activity at moderately low temperatures. Forexample, the type 1 component may comprise a C2+ yield of greater than5% or greater than 10% at temperatures less than 800° C., less than 700°C. or less than 600° C. The type 2 component may comprise a C2+ yieldless than 0.1%, less than 1% or less than 5% at temperatures less than800° C., less than 700° C. or less than 600° C. The type 2 component maycomprise a C2+ yield of greater than 0.1%, greater than 1%, greater than5% or greater than 10% at temperatures greater than 800° C., greaterthan 700° C. or greater than 600° C. Typical type 1 components includeany of the catalysts as described herein, while typical type 2components include bulk OCM catalysts and nanowire catalysts which onlyhave good OCM activity at higher temperatures, for example greater than800° C. Examples of type 2 components may include catalysts comprisingMgO. The catalyst blend may further comprise inert support materials asdescribed above (e.g., silica, alumina, silicon carbide, etc.).

In certain embodiments, the type 2 component acts as diluent in the sameway an inert material does and thus helps reduce and/or control hotspots in the catalyst bed caused by the exothermic nature of the OCMreaction. However, because the type 2 component is an OCM catalyst,albeit not a particularly active one, it may prevent the occurrence ofundesired side reactions, e.g., methyl radical quenching. Additionally,controlling the hotspots has the beneficial effect of extending thelifetime of the catalyst.

For example, it has been found that diluting active lanthanide oxide OCMcatalysts with as much as a 10:1 ratio of MgO, which by itself is not anactive OCM catalyst at the temperature which the lanthanide oxideoperates, is a good way to minimize “hot spots” in the reactor catalystbed, while maintaining the selectivity and yield performance of thecatalyst. On the other hand, doing the same dilution with quartz SiO₂ isnot effective because it appears to quench the methyl radicals whichserves to lower the selectivity to C2s.

In yet another embodiment, the type 2 components are good oxidativedehydrogenation (ODH) catalysts at the same temperature that the type 1components are good OCM catalysts. In this embodiment, theethylene/ethane ratio of the resulting gas mixture can be tuned in favorof higher ethylene. In another embodiment, the type 2 components are notonly good ODH catalysts at the same temperature the type 1 componentsare good OCM catalysts, but also have limited to moderate OCM activityat these temperatures.

In related embodiments, the catalytic performance of the catalyticmaterial is tuned by selecting specific type 1 and type 2 components ofa catalyst blend. In another embodiment, the catalytic performance istuned by adjusting the ratio of the type 1 and type 2 components in thecatalytic material. For example, the type 1 catalyst may be a catalystfor a specific step in the catalytic reaction, while the type 2 catalystmay be specific for a different step in the catalytic reaction. Forexample, the type 1 catalyst may be optimized for formation of methylradicals and the type 2 catalyst may be optimized for formation ofethane or ethylene.

In other embodiments, the catalytic material comprises at least twodifferent components (component 1, component 2, component 3, etc.). Thedifferent components may comprise different morphologies, e.g.,nanowires, nanoparticles, bulk, etc. The different components in thecatalyst material can be, but not necessarily, of the same chemicalcomposition and the only difference is in the morphology and/or the sizeof the particles. This difference in morphology and particle size mayresult in a difference in reactivity at a specific temperature.Additionally, the difference in morphology and particle size of thecatalytic material components is advantageous for creating a veryintimate blending, e.g., very dense packing of the catalysts particles,which can have a beneficial effect on catalyst performance. Also, thedifference in morphology and particle size of the blend components wouldallow for control and tuning of the macro-pore distribution in thereactor bed and thus its catalytic efficiency. An additional level ofmicro-pore tuning can be attained by blending catalysts with differentchemical composition and different morphology and/or particle size. Theproximity effect would be advantageous for the reaction selectivity.

Accordingly, in one embodiment the present disclosure provides the useof a catalytic material comprising a first catalyst and a secondcatalyst, for example a first catalytic nanowire and a bulk catalystand/or a second catalytic nanowire, in a catalytic reaction, for examplethe catalytic reaction may be OCM or ODH. In other embodiments, thefirst catalytic nanowire and the bulk catalyst and/or second catalyticnanowire are each catalytic with respect to the same reaction, and inother examples the first catalytic nanowire and the bulk catalyst and/orsecond catalytic nanowire have the same chemical composition.

In some specific embodiments of the foregoing, the catalytic materialcomprises a first catalytic nanowire and a second catalytic nanowire.Each nanowire can have completely different chemical compositions orthey may have the same base composition and differ only by the dopingelements. In other embodiments, each nanowire can have the same or adifferent morphology. For example, each nanowire can differ by thenanowire size (length and/or aspect ratio), by ratio of actual/effectivelength, by chemical composition or any combination thereof. Furthermore,the first and second nanowires may each be catalytic with respect to thesame reaction but may have different activity. Alternatively, eachnanowire may catalyze different reactions.

In a related embodiment, the catalytic material comprises a firstcatalytic nanowire and a bulk catalyst. The first nanowire and the bulkcatalyst can have completely different chemical compositions or they mayhave the same base composition and differ only by the doping elements.Furthermore, the first nanowire and the bulk catalyst may each becatalytic with respect to the same reaction but may have differentactivity. Alternatively, the first nanowire and the bulk catalyst maycatalyze different reactions.

In yet other embodiments of the foregoing, the catalytic nanowire has acatalytic activity in the catalytic reaction, which is greater than acatalytic activity of the bulk catalyst in the catalytic reaction at thesame temperature. In still other embodiments, the catalytic activity ofthe bulk catalyst in the catalytic reaction increases with increasingtemperature.

OCM catalysts may be prone to hotspots due to the very exothermic natureof the OCM reaction. Diluting such catalysts helps to manage thehotspots. However, the diluent needs to be carefully chosen so that theoverall performance of the catalyst is not degraded. Silicon carbide forexample can be used as a diluent with little impact on the OCMselectivity of the blended catalytic material whereas using silica as adiluent significantly reduces OCM selectivity. The good heatconductivity of SiC is also beneficial in minimizing hot spots. As notedabove, use of a catalyst diluents or support material that is itself OCMactive has significant advantages over more traditional diluents such assilica and alumina, which can quench methyl radicals and thus reduce theOCM performance of the catalyst. An OCM active diluent is not expectedto have any adverse impact on the generation and lifetime of methylradicals and thus the dilution should not have any adverse impact on thecatalyst performance. Thus embodiments of the invention include catalystcompositions comprising an OCM catalyst (e.g., any of the disclosedcatalysts) in combination with a diluent or support material that isalso OCM active. Methods for use of the same in an OCM reaction are alsoprovided.

In some embodiments, the above diluent comprises alkaline earth metalcompounds, for example alkaline metal oxides, carbonates, sulfates orphosphates. Examples of diluents useful in various embodiments include,but are not limited to, MgO, MgCO₃, MgSO₄, Mg₃(PO₄)₂, MgAl₂O₄, CaO,CaCO₃, CaSO₄, Ca₃(PO₄)₂, CaAl₂O₄, SrO, SrCO₃, Sr₅O₄, Sr₃(PO₄)₂, SrAl₂O₄,BaO, BaCO₃, BaSO₄, Ba₃(PO₄)₂, BaAl₂O₄ and the like. Most of thesecompounds are very cheap, especially MgO, CaO, MgCO₃, CaCO₃, SrO, SrCO₃and thus very attractive for use as diluents from an economic point ofview. Additionally, the magnesium, calcium and strontium compounds areenvironmentally friendly too. Accordingly, an embodiment of theinvention provides a catalytic material comprising a catalyst incombination with a diluent selected from one or more of MgO, MgCO₃,MgSO₄, Mg₃(PO₄)₂, CaO, CaCO₃, CaSO₄, Ca₃(PO₄)₂, SrO, SrCO₃, SrSO₄,Sr₃(PO₄)₂, BaO, BaCO₃, BaSO₄, Ba₃(PO₄)₂. In some specific embodimentsthe diluents is MgO, CaO, SrO, MgCO₃, CaCO₃, SrCO₃ or combinationthereof. Methods for use of the foregoing catalytic materials in an OCMreaction are also provided. The methods comprise converting methane toethane and or ethylene in the presence of the catalytic materials.

The above diluents and supports may be employed in any number ofmethods. For example, in some embodiments a support (e.g., MgO, CaO,CaCO₃, SrCO₃) may be used in the form of a pellet or monolith (e.g.,honeycomb) structure, and the catalysts may be impregnated or supportedthereon. In other embodiments, a core/shell arrangement is provided andthe support material may form part of the core or shell. For example, acore of MgO, CaO, CaCO₃ or SrCO₃ may be coated with a shell of any ofthe disclosed catalyst compositions.

In some embodiments, the diluent has a morphology selected from bulk(e.g., commercial grade), nano (nanowires, nanorods, nanoparticles,etc.) or combinations thereof.

In some embodiments, the diluent has none to moderate catalytic activityat the temperature the OCM catalyst is operated. In some otherembodiments, the diluent has moderate to large catalytic activity at atemperature higher than the temperature the OCM catalyst is operated. Inyet some other embodiments, the diluent has none to moderate catalyticactivity at the temperature the OCM catalyst is operated and moderate tolarge catalytic activity at temperatures higher than the temperature theOCM catalyst is operated. Typical temperatures for operating an OCMreaction according to the present disclosure are 800° C. or lower, 750°C. or lower, 700° C. or lower, 650° C. or lower, 600° C. or lower and550° C. or lower.

For example, CaCO₃ is a relatively good OCM catalyst at T>750° C. (50%selectivity, >20% conversion) but has essentially no activity below 700°C. Experiments performed in support of the present invention showed thatdilution of Nd₂O₃ straight nanowires with CaCO₃ or SrCO₃ (bulk) showedno degradation of OCM performance and, in some cases, even betterperformance than the neat catalyst.

In some embodiments, the diluent portion in the catalyst/diluent mixtureis 0.01%, 10%, 30%, 50%, 70%, 90% or 99.99% (weight percent) or anyother value between 0.01% and 99.9%. In some embodiments, the dilutionis performed with the OCM catalyst ready to go, e.g., after calcination.In some other embodiments, the dilution is performed prior to the finalcalcination of the catalyst, i.e., the catalyst and the diluent arecalcined together. In yet some other embodiments, the dilution can bedone during the synthesis as well, so that, for example, a mixed oxideis formed.

In some embodiments, the catalyst/diluent mixture comprises more thanone catalyst and/or more than one diluent. In some other embodiments,the catalyst/diluent mixture is pelletized and sized, or made intoshaped extrudates or deposited on a monolith or foam, or is used as itis. Methods of the invention include taking advantage of the veryexothermic nature of OCM by diluting the catalyst with another catalystthat is (almost) inactive in the OCM reaction at the operatingtemperature of the first catalyst but active at higher temperature. Inthese methods, the heat generated by the hotspots of the first catalystwill provide the necessary heat for the second catalyst to becomeactive.

For ease of illustration, the above description of catalytic materialsoften refers to OCM; however, such catalytic materials find utility inother catalytic reactions including but not limited to: oxidativedehydrogenation (ODH) of alkanes to their corresponding alkenes,selective oxidation of alkanes and alkenes and alkynes, oxidation of co,dry reforming of methane, selective oxidation of aromatics,Fischer-Tropsch, combustion of hydrocarbons, etc.

3. Preparation of Catalysts and Catalytic Materials

The catalysts can be prepared using any suitable method (e.g., such thatthe catalyst functions as an OCM catalyst). Suitable methods, whichinclude using a bacteriophage template and other methods known in theart, are described in U.S. application Ser. No. 13/115,082 (U.S. Pub.No. 2012/0041246), Ser. No. 13/689,514 (U.S. Pub. No. 2013/0158322) andSer. No. 13/689,611 (U.S. Pub. No. 2013/0165728), which applications arehereby incorporated by reference in their entireties.

In some embodiments, the nanowire catalysts can be synthesized in asolution phase in the absence of a template. Typically, a hydrothermalor sol gel approach can be used to create straight (i.e., ratio ofeffective length to actual length equal to one) and substantially singlecrystalline nanowires. As an example, nanowires comprising a metal oxidecan be prepared by (1) forming nanowires of a metal oxide precursor(e.g., metal hydroxide) in a solution of a metal salt and an anionprecursor; (2) isolating the nanowires of the metal oxide precursor; and(3) calcining the nanowires of the metal oxide precursor to providenanowires of a corresponding metal oxide. In other embodiments (forexample MgO nanowires), the synthesis goes through an intermediate whichcan be prepared as a nanowire and then converted into the desiredproduct while maintaining its morphology. Optionally, the nanowirescomprising a metal oxide can be doped according to methods describedherein.

In other certain embodiments, nanowires comprising a core/shellstructure are prepared in the absence of a biological template. Suchmethods may include, for example, preparing a nanowire comprising afirst metal and growing a shell on the outersurface of this nanowire,wherein the shell comprises a second metal. The first and second metalsmay be the same or different.

In other aspects, a core/shell nanowire is prepared in the absence of abiological template. Such methods comprise preparing a nanowirecomprising an inner core and an outer shell, wherein the inner corecomprises a first metal, and the outer shell comprises a second metal,the method comprising:

-   -   a) preparing a first nanowire comprising the first metal; and    -   b) treating the first nanowire with a salt comprising the second        metal.

In some embodiments of the foregoing method, the method furthercomprises addition of a base to a solution obtained in step b). In yetother examples, the first metal and the second metal are different. Inyet further embodiments, the salt comprising the second metal is ahalide or a nitrate. In certain aspects it may be advantageous toperform one or more sequential additions of the salt comprising thesecond metal and a base. Such sequential additions help preventnon-selective precipitation of the second metal and favor conditionswherein the second metal nucleates on the surface of the first nanowireto form a shell of the second metal. Furthermore, the first nanowire maybe prepared by any method, for example via a template directed method(e.g., phage).

As with template-directed syntheses, the synthetic conditions andparameters for direct synthesis (template free) of nanowires can also beadjusted to create diverse compositions and surface morphologies (e.g.,crystal faces) and dopant levels. For example, variable syntheticparameters include: concentration ratios of metal and anions (e.g.,hydroxide); reaction temperature; reaction time; sequence of addinganion and metal ions; pH; types of metal precursor salt; types of anionprecursor; number of additions; the time that lapses between theadditions of the metal salt and anion precursor, including, e.g.,simultaneous (zero lapse) or sequential additions followed by respectiveincubation times for the metal salt and the anion precursor.

In addition, the choice of solvents or surfactants may influence thecrystal growth of the nanowires, thereby generating different nanowiredimensions (including aspect ratios). For example, solvents such asethylene glycol, poly(ethylene glycol), polypropylene glycol andpoly(vinyl pyrrolidone) can serve to passivate the surface of thegrowing nanowires and facilitate a linear growth of the nanowire.

In some embodiments, nanowires can be prepared directly from thecorresponding oxide. For example, metal oxides may be treated withhalides, for example ammonium halides, to produce nanowires. Suchembodiments find particular utility in the context of lanthanide oxides,for example La₂O₃, are particularly useful since the procedure is quitesimple and economically efficient Nanowires comprising two or moremetals and/or dopants may also be prepared according to these methods.Accordingly, in some embodiments at least one of the metal compounds isan oxide of a lanthanide element.

Accordingly, in one embodiment the present disclosure provides a methodfor preparing a nanowire in the absence of a biological template, themethod comprising treating at least one metal compound with a halide. Incertain embodiments, nanowires comprising more than one type of metaland/or one or more dopants can be prepared by such methods. For example,in one embodiment the method comprises treating two or more differentmetal compounds with a halide and the nanowire comprises two or moredifferent metals. The nanowire may comprise a mixed metal oxide, metaloxyhalide, metal oxynitrate or metal sulfate.

In some other embodiments of the foregoing, the halide is in the form ofan ammonium halide. In yet other embodiments, the halide is contactedwith the metal compound in solution or in the solid state.

In certain embodiments, the method is useful for incorporation of one ormore doping elements into a nanowire. For example, the method maycomprise treating at least one metal compound with a halide in thepresence of at least one doping element, and the nanowire comprises theleast one doping element. In some aspects, the at least one dopingelement is present in the nanowire in an atomic percent ranging from 0.1to 50 at %.

Other methods for preparation of nanowires in the absence of abiological template include preparing a hydroxide gel by reaction of atleast one metal salt and a hydroxide base. For example, the method mayfurther comprise aging the gel, heating the gel or combinations thereof.In certain other embodiments, the method comprises reaction of two ormore different metal salts, and the nanowire comprises two or moredifferent metals.

Doping elements may also be incorporated by using the hydroxide gelmethod described above, further comprising addition of at least onedoping element to the hydroxide gel, and wherein the nanowire comprisesthe at least one doping element. For example, the at least one dopingelement may be present in the nanowire in an atomic percent ranging from0.1 to 50 at %.

In some embodiments, metal oxide nanowires can be prepared by mixing ametal salt solution and an anion precursor so that a gel of a metaloxide precursor is formed. This method can work for cases where thetypical morphology of the metal oxide precursor is a nanowire. The gelis thermally treated so that crystalline nanowires of the metal oxideprecursor are formed. The metal oxide precursor nanowires are convertedto metal oxide nanowires by calcination. This method can be especiallyuseful for lanthanides and group 3 elements. In some embodiments, thethermal treatment of the gel is hydrothermal (or solvothermal) attemperatures above the boiling point of the reaction mixture and atpressures above ambient pressure, in other embodiments it's done atambient pressure and at temperatures equal to or below the boiling pointof the reaction mixture. In some embodiments the thermal treatment isdone under reflux conditions at temperatures equal to the boiling pointof the mixture. In some specific embodiments the anion precursor is ahydroxide, e.g., Ammonium hydroxide, sodium hydroxide, lithiumhydroxide, tetramethyl ammonium hydroxide, and the like. In some otherspecific embodiments the metal salt is LnCl₃ (Ln=Lanthanide), in otherembodiment the metal salt is Ln(NO₃)₃. In yet other embodiments, themetal salt is YCl₃, ScCl₃, Y(NO₃)₃, Sc(NO₃)₃. In some other embodiments,the metal precursor solution is an aqueous solution. In otherembodiments, the thermal treatment is done at T=100° C. under refluxconditions.

This method can be used to make mixed metal oxide nanowires, by mixingat least two metal salt solutions and an anion precursor so that a mixedoxide precursor gel is formed. In such cases, the first metal may be alathanide or a group 3 element, and the other metals can be from othergroups, including groups 1-14.

In some different embodiments, metal oxide nanowires can be prepared ina similar way as described above by mixing a metal salt solution and ananion precursor so that a gel of a metal hydroxide precursor is formed.This method works for cases where the typical morphology of the metalhydroxide precursor is a nanowire. The gel is treated so thatcrystalline nanowires of the metal hydroxide precursor are formed. Themetal hydroxide precursor nanowires are converted to metal hydroxidenanowires by base treatment and finally converted to metal oxidenanowires by calcination. This method may be especially applicable forgroup 2 elements, for example Mg. In some specific embodiments, the geltreatment is a thermal treatment at temperatures in the range 50-100° C.followed by hydrothermal treatment. In other embodiments, the geltreatment is an aging step. In some embodiments, the aging step takes atleast one day. In some specific embodiments, the metal salt solution isa concentrated metal chloride aqueous solution and the anion precursoris the metal oxide. In some more specific embodiments, the metal is Mg.In certain embodiments of the above, these methods can be used to makemixed metal oxide nanowires. In these embodiments, the first metal is Mgand the other metal can be any other metal of groups 1-14+Ln.

The catalysts and/or catalytic materials can be prepared according toany number of methods known in the art. For example, the catalystsand/or catalytic materials can be prepared after preparation of theindividual components by mixing the individual components in their dryform, e.g., blend of powders, and optionally, ball milling can be usedto reduce particle size and/or increase mixing. Each component can beadded together or one after the other to form layered particles.Alternatively, the individual components can be mixed prior tocalcination, after calcination or by mixing already calcined componentswith uncalcined components. The catalysts and/or catalytic materials mayalso be prepared by mixing the individual components in their dry formand optionally pressing them together into a “pill” followed bycalcination to above 400° C.

The foregoing catalysts may be doped prior to, or after formation of thecatalyst. In one embodiment, one or more metal salts are mixed to form asolution or a slurry which is dried and then calcined in a range of 400°C. to 900° C., or between 500° C. and 700° C. In another embodiment, thecatalyst is formed first through calcination of one or more metal saltfollowed by contact with a solution comprising the doping elementfollowed by drying and/or calcination between 300° C. and 800° C., orbetween 400° C. and 700° C.

In other examples, the catalysts and/or catalytic materials are preparedby mixing the individual components with one or more solvents into asolution, suspension or slurry. Optional mixing and/or ball milling canbe used to maximize uniformity and reduce particle size. Examples ofsolvents useful in this context include, but are not limited to: water,alcohols, ethers, carboxylic acids, ketones, esters, amides, aldehydes,amines, alkanes, alkenes, alkynes, aromatics, etc. In other embodiments,the individual components are deposited on a supporting material such assilica, alumina, magnesia, activated carbon, and the like, or by mixingthe individual components using a fluidized bed granulator. Combinationsof any of the above methods may also be used.

The catalysts and/or catalytic materials may optionally comprise adopant as described in more detail herein. In this respect, dopingmaterial(s) may be added during preparation of the individualcomponents, after preparation of the individual components but beforedrying of the same, after the drying step but before calcinations orafter calcination. If more than one doping material is used, each dopantcan be added together or one after the other to form layers of dopants.

Doping material(s) may also be added as dry components and optionallyball milling can be used to increase mixing. In other embodiments,doping material(s) are added as a liquid (e.g., solution, suspension,slurry, etc.) to the dry individual catalyst components or to theblended catalytic material. The amount of liquid may optionally beadjusted for optimum wetting of the catalyst, which can result inoptimum coverage of catalyst particles by doping material. Mixing and/orball milling can also be used to maximize doping coverage and uniformdistribution. Alternatively, doping material(s) are added as a liquid(e.g., solution, suspension, slurry, etc.) to a suspension or slurry ofthe catalyst in a solvent. Mixing and/or ball milling can be used tomaximize doping coverage and uniform distribution. Incorporation ofdopants can also be achieved using any of the methods describedelsewhere herein.

As noted herein, an optional calcination step usually follows anoptional drying step at T<200 C (typically 60-120 C) in a regular ovenor in a vacuum oven. Calcination may be performed on the individualcomponents of the catalysts and/or catalytic material or on the blendedcatalysts and/or catalytic material. Calcination is generally performedin an oven/furnace at a temperature higher than the minimum temperatureat which at least one of the components decomposes or undergoes a phasetransformation and can be performed in inert atmosphere (e.g., N₂, Ar,He, etc.), oxidizing atmosphere (air, O₂, etc.) or reducing atmosphere(H₂, H₂/N₂, H₂/Ar, etc.). The atmosphere may be a static atmosphere or agas flow and may be performed at ambient pressure, at p<1 atm, in vacuumor at p>1 atm. High pressure treatment (at any temperature) may also beused to induce phase transformation including amorphous to crystalline.Calcinations may also be performed using microwave heating.

Calcination is generally performed in any combination of stepscomprising ramp up, dwell and ramp down. For example, ramp to 500° C.,dwell at 500° C. for 5 h, ramp down to RT. Another example includes rampto 100° C., dwell at 100° C. for 2 h, ramp to 300° C., dwell at 300° C.for 4 h, ramp to 550° C., dwell at 550° C. for 4 h, ramp down to RT.Calcination conditions (pressure, atmosphere type, etc.) can be changedduring the calcination. In some embodiments, calcination is performedbefore preparation of the blended catalytic material (i.e., individualcomponents are calcined), after preparation of the blended catalyticmaterial but before doping, after doping of the individual components orblended catalytic material. Calcination may also be performed multipletimes, e.g., after catalyst preparation and after doping.

The catalytic materials may be incorporated into a reactor bed forperforming any number of catalytic reactions (e.g., OCM, ODH and thelike). Accordingly, in one embodiment the present disclosure provides acatalytic material as disclosed herein in contact with a reactor and/orin a reactor bed. For example, the reactor may be for performing an OCMreaction, may be a fixed bed reactor and may have a diameter greaterthan 1 inch. In this regard, the catalytic material may be packed neat(without diluents) or diluted with an inert material (e.g., sand,silica, alumina, etc.) The catalyst components may be packed uniformlyforming a homogeneous reactor bed.

The particle size of the individual components within a catalyticmaterial may also alter the catalytic activity, and other properties, ofthe same. Accordingly, in one embodiment, the catalyst is milled to atarget average particle size or the catalyst powder is sieved to selecta particular particle size. In some aspects, the catalyst powder may bepressed into pellets and the catalyst pellets can be optionally milledand or sieved to obtain the desired particle size distribution.

In some embodiments, the catalyst materials, alone or with bindersand/or diluents, can be configured into larger aggregate forms, such aspellets, extrudates, or other aggregations of catalyst particles. Forease of discussion, such larger forms are generally referred to hereinas “pellets”. Such pellets may optionally include a binder and/orsupport material; however, the present inventors have surprisingly foundthat the disclosed nanowires are particularly suited to use in the formof a pellet without a binder and/or support material. Accordingly, oneembodiment of the disclosure provides a catalytic material in theabsence of a binder. In this regard, the morphology of the disclosednanowires (either bent or straight, etc.) is believed to contribute tothe nanowires' ability to be pressed into pellets without the need for abinder. Catalytic materials without binders are simpler, less complexand cheaper than corresponding materials with binders and thus offercertain advantages.

In some instances, catalytic materials may be prepared using a“sacrificial binder” or support. Because of their special properties,the nanowires allow for preparation of catalytic material forms (e.g.,pellets) without the use of a binder. A “sacrificial” binder can be usedin order to create unique microporosity in pellets or extrudates. Afterremoving the sacrificial binder, the structural integrity of thecatalyst is ensured by the special binding properties of the nanowiresand the resulting catalytic material has unique microporosity as aresult of removing the binder. For example, in some embodiments acatalytic nanowire may be prepared with a binder and then the binderremoved by any number of techniques (e.g., calcinations, acid erosion,etc.). This method allows for design and preparation of catalyticmaterials having unique microporosity (i.e., the microporosity is afunction of size, etc., of the sacrificial binder). The ability toprepare different forms (e.g., pellets) of the nanowires without the useof binder is not only useful for preparation of catalytic materials fromthe nanowires, but also allows the nanowires to be used as supportmaterials (or both catalytic and support material). Sacrificial bindersand techniques useful in this regard include sacrificial cellulosicfibers or other organic polymers that can be easily removed bycalcination, non-sacrificial binders and techniques useful in thisregard include, colloidal oxide binders such as Ludox Silica or Nyacolcolloidal zirconia that can also be added to strengthen the formedaggregate when needed. Sacrificial binders are added to increasemacro-porosity (pores larger than 20 nm diameter) of the catalyticmaterials. Accordingly, in some embodiments the catalytic materialscomprise pores greater than 20 nm in diameter, greater than 50 nm indiameter, greater than 75 nm in diameter, greater than 100 nm indiameter or greater than 150 nm in diameter.

Catalytic materials also include any of the disclosed catalysts disposedon or adhered to a solid support. For example, the catalysts may beadhered to the surface of a monolith support. As with the binder-lessmaterials discussed above, in these embodiments the catalysts may beadhered to the surface of the monolith in the absence of a binder due totheir unique morphology and packing properties. Monoliths includehoneycomb-type structures, foams and other catalytic support structuresderivable by one skilled in the art. In one embodiment, the support is ahoneycomb matrix formed from silicon carbide, and the support furthercomprises the disclosed catalyst disposed on the surface.

As the OCM reaction is very exothermic, it can be desirable to reducethe rate of conversion per unit volume of reactor in order to avoid runaway temperature rise in the catalyst bed that can result in hot spotsaffecting performance and catalyst life. One way to reduce the OCMreaction rate per unit volume of reactor is to spread the activecatalyst onto an inert support with interconnected large pores as inceramic or metallic foams (including metal alloys having reducedreactivity with hydrocarbons under OCM reaction conditions) or havingarrays of channel as in honeycomb structured ceramic or metal assembly.

In one embodiment, a catalytic material comprising a catalyst asdisclosed herein supported on a structured support is provided. Examplesof such structure supports include, but are not limited to, metal foams,Silicon Carbide or Alumina foams, corrugated metal foil arranged to formchannel arrays, extruded ceramic honeycomb, for example Cordierite(available from Corning or NGK ceramics, USA), Silicon Carbide orAlumina.

Active catalyst loading on the structured support ranges from 1 to 500mg per ml of support component, for example from 5 to 100 mg per ml ofstructure support. Cell densities on honeycomb structured supportmaterials may range from 100 to 900 CPSI (cell per square inch), forexample 200 to 600 CPSI. Foam densities may range from 10 to 100 PPI(pore per inch), for example 20 to 60 PPI.

In other embodiments, the exotherm of the OCM reaction may be at leastpartially controlled by blending the active catalytic material withcatalytically inert material, and pressing or extruding the mixture intoshaped pellets or extrudates. In some embodiments, these mixed particlesmay then be loaded into a pack-bed reactor. The Extrudates or pelletscomprise between 30% to 70% pore volume with 5% to 50% active catalystweight fraction. Useful inert materials in this regard include, but arenot limited to MgO, CaO, Al₂O₃, SiC and cordierite.

In addition to reducing the potential for hot spots within the catalyticreactor, another advantage of using a structured ceramic with large porevolume as a catalytic support is reduced flow resistance at the same gashourly space velocity versus a pack-bed containing the same amount ofcatalyst.

Yet another advantage of using such supports is that the structuredsupport can be used to provide features difficult to obtain in apack-bed reactor. For example the support structure can improve mixingor enabling patterning of the active catalyst depositions through thereactor volume. Such patterning can consist of depositing multiplelayers of catalytic materials on the support in addition to the OCMactive component in order to affect transport to the catalyst orcombining catalytic functions as adding O₂—ODH activity, CO₂—OCMactivity or CO₂—ODH activity to the system in addition to O₂—OCM activematerial. Another patterning strategy can be to create bypass within thestructure catalyst essentially free of active catalyst to limit theoverall conversion within a given supported catalyst volume.

Yet another advantage is reduced heat capacity of the bed of thestructured catalyst over a pack bed a similar active catalyst loadingtherefore reducing startup time.

Nanowire shaped catalysts are particularly well suited for incorporationinto pellets or extrudates or deposition onto structured supports.Nanowire aggregates forming a mesh type structure can have good adhesiononto rough surfaces.

The mesh like structure can also provide improved cohesion in compositeceramic improving the mechanical properties of pellets or extrudatescontaining the nanowire shaped catalyst particles.

Alternatively, such nanowire on support or in pellet form approaches canbe used for other reactions besides OCM, such as ODH, dry methanereforming, FT, and all other catalytic reactions.

In yet another embodiment, the catalysts are packed in bands forming alayered reactor bed. Each layer is composed by either a catalyst of aparticular type, morphology or size or a particular blend of catalysts.In one embodiment, the catalysts blend may have better sinteringproperties, i.e., lower tendency to sinter, then a material in its pureform. Better sintering resistance is expected to increase the catalyst'slifetime and improve the mechanical properties of the reactor bed.

In yet other embodiments, the disclosure provides a catalytic materialcomprising one or more different catalysts. The catalysts may be ananowire as disclosed herein and a different catalyst for example a bulkcatalysts. Mixtures of two or more nanowire catalysts are alsocontemplated. The catalytic material may comprise a catalyst, forexample a nanowire catalyst, having good OCM activity and a catalysthaving good activity in the ODH reaction. Either one or both of thesecatalysts may be nanowires as disclosed herein.

One skilled in the art will recognize that various combinations oralternatives of the above methods are possible, and such variations arealso included within the scope of the present disclosure.

4. Structure/Physical Characteristics of the Disclosed Catalysts

Typically, a catalytic material described herein comprises a pluralityof metal oxide particles. In certain embodiments, the catalytic materialmay further comprise a support material. The total surface area per gramof a catalytic material may have an effect on the catalytic performance.Pore size distribution may affect the catalytic performance as well.Surface area and pore size distribution of the catalytic material can bedetermined by BET (Brunauer, Emmett, Teller) measurements. BETtechniques utilize nitrogen adsorption at various temperatures andpartial pressures to determine the surface area and pore sizes ofcatalysts. BET techniques for determining surface area and pore sizedistribution are well known in the art.

In some embodiments the catalytic material comprises a surface area ofbetween 0.1 and 100 m²/g, between 1 and 100 m²/g, between 1 and 50 m²/g,between 1 and 20 m²/g, between 1 and 10 m²/g, between 1 and 5 m²/g,between 1 and 4 m²/g, between 1 and 3 m²/g, or between 1 and 2 m²/g.

Additional structural properties of the catalysts and catalyticmaterials are described in U.S. application Ser. No. 13/115,082 (U.S.Pub. No. 2012/0041246), Ser. No. 13/689,514 (U.S. Pub. No. 2013/0158322)and Ser. No. 13/689,611 (U.S. Pub. No. 2013/0165728), which applicationsare hereby incorporated by reference in their entireties.

Catalytic Reactions

The present disclosure provides heterogeneous catalysts having bettercatalytic properties than known catalysts. The catalysts disclosedherein are useful in any number of reactions catalyzed by aheterogeneous catalyst. Examples of reactions wherein the disclosedcatalysts may be employed are disclosed in Farrauto and Bartholomew,“Fundamentals of Industrial Catalytic Processes” Blackie Academic andProfessional, first edition, 1997, which is hereby incorporated in itsentirety. Other non-limiting examples of reactions wherein the catalystsmay be employed include: the oxidative coupling of methane (OCM) toethane and ethylene; oxidative dehydrogenation (ODH) of alkanes to thecorresponding alkenes, for example oxidative dehydrogenation of ethaneor propane to ethylene or propylene, respectively; selective oxidationof alkanes, alkenes, and alkynes; oxidation of CO, dry reforming ofmethane, selective oxidation of aromatics; Fischer-Tropsch, hydrocarboncracking; combustion of hydrocarbons and the like. Reactions catalyzedby the disclosed catalysts are discussed in more detail below. While anembodiment of the invention is described in greater detail below in thecontext of the OCM reaction and other reactions described herein, thecatalysts are not in any way limited to the particularly describedreactions.

The disclosed catalysts are generally useful in methods for converting afirst carbon-containing compound (e.g., a hydrocarbon, CO or CO₂) to asecond carbon-containing compound. In some embodiments the methodscomprise contacting a disclosed catalyst, or material comprising thesame, with a gas comprising a first carbon-containing compound and anoxidant to produce a second carbon-containing compound. In someembodiments, the first carbon-containing compound is a hydrocarbon, CO,CO₂, methane, ethane, propane, hexane, cyclohexane, octane orcombinations thereof. In other embodiments, the second carbon-containingcompound is a hydrocarbon, CO, CO₂, ethane, ethylene, propane,propylene, hexane, hexene, cyclohexane, cyclohexene, bicyclohexane,octane, octene or hexadecane. In some embodiments, the oxidant isoxygen, ozone, nitrous oxide, nitric oxide, water, carbon dioxide orcombinations thereof.

In other embodiments of the foregoing, the method for conversion of afirst carbon-containing compound to a second carbon-containing compoundis performed at a temperature below 100° C., below 200° C., below 300°C., below 400° C., below 500° C., below 550° C., below 600° C., below700° C., below 800° C., below 900° C. or below 1000° C. In certainembodiments, the method is OCM and the method is performed at atemperature below 600° C., below 700° C., below 800° C., or below 900°C. In other embodiments, the method for conversion of a firstcarbon-containing compound to a second carbon-containing compound isperformed at a pressure above 0.5 atm, above 1 atm, above 2 atm, above 5atm, above 10 atm, above 15 atm above 25 atm or above 50 atm.

The catalytic reactions described herein can be performed using standardlaboratory equipment known to those of skill in the art, for example asdescribed in U.S. Pat. No. 6,350,716, which is incorporated herein inits entirety.

As noted above, the catalysts disclosed herein have better catalyticactivity than a corresponding undoped catalyst. In some embodiments, theselectivity, yield, conversion, or combinations thereof, of a reactioncatalyzed by the catalysts is better than the selectivity, yield,conversion, or combinations thereof, of the same reaction catalyzed by acorresponding undoped catalyst under the same conditions. For example,in some embodiments, the catalysts are doped bulk catalysts or nanowirecatalysts (doped or undoped) and the catalysts possess a catalyticactivity such that conversion of reactant to product in a reactioncatalyzed by the catalyst is at least 1.1 times, at least 1.25 times, atleast 1.5 times, at least 2.0 times, at least 3.0 times or at least 4.0times the yield of product in the same reaction under the sameconditions but catalyzed by a corresponding catalyst. As used herein a“corresponding catalyst” refers to:

1) an undoped bulk catalyst (i.e., a catalyst comprising the same basematerial but different or no dopants or different ratios orconcentrations of the same dopants) when the comparison is to a dopedbulk catalyst of the invention;

2) a bulk catalyst (i.e., a catalyst prepared from bulk material havingthe same chemical composition as the nanowire, including any dopants)when the comparison is to a doped or undoped nanowire catalyst of theinvention; or

3) an undoped nanowire catalyst when the comparison is to a dopednanowire of the invention.

For purpose of clarity, it should be noted that this comparison (andothers throughout the application) is made to an undoped bulk catalystwhen the catalysts are doped bulk catalysts and to a corresponding bulkcatalyst when the catalysts are nanowire catalysts.

In other embodiments, the catalysts are doped bulk catalysts or nanowirecatalysts (doped or undoped) and the catalysts possess a catalyticactivity such that selectivity for product in a reaction catalyzed bythe catalyst is at least 1.1 times, at least 1.25 times, at least 1.5times, at least 2.0 times, at least 3.0 times or at least 4.0 times theyield of product in the same reaction under the same conditions butcatalyzed by a corresponding catalyst.

In yet other embodiments, the catalysts are doped bulk catalysts ornanowire catalysts (doped or undoped) and the catalysts possess acatalytic activity such that yield of product in a reaction catalyzed bythe catalyst is at least 1.1 times, at least 1.25 times, at least 1.5times, at least 2.0 times, at least 3.0 times or at least 4.0 times theyield of product in the same reaction under the same conditions butcatalyzed by a corresponding catalyst. In yet other embodiments, thecatalysts are doped bulk catalysts or nanowire catalysts (doped orundoped) and the catalysts possess a catalytic activity such that theactivation temperature of a reaction catalyzed by the catalyst is atleast 25° C. lower, at least 50° C. lower, at least 75° C. lower, or atleast 100° C. lower than the temperature of the same reaction under thesame conditions but catalyzed by a corresponding catalyst. In certainreactions (e.g., OCM), production of unwanted oxides of carbon (e.g., COand CO₂) is a problem that reduces overall yield of desired product andresults in an environmental liability. Accordingly, in one embodimentthe present disclosure addresses this problem and provides catalystswith a catalytic activity such that the selectivity for CO and/or CO₂ ina reaction catalyzed by the catalysts is less than the selectivity forCO and/or CO₂ in the same reaction under the same conditions butcatalyzed by an undoped catalyst. Accordingly, in one embodiment, thepresent disclosure provides a doped bulk catalysts or nanowire catalysts(doped or undoped) and the catalysts possess a catalytic activity suchthat selectivity for CON, wherein x is 1 or 2, in a reaction catalyzedby the catalyst is less than at least 0.9 times, less than at least 0.8times, less than at least 0.5 times, less than at least 0.2 times orless than at least 0.1 times the selectivity for CO_(x) in the samereaction under the same conditions but catalyzed by a correspondingcatalyst.

In some embodiments, the absolute selectivity, yield, conversion, orcombinations thereof, of a reaction catalyzed by the catalysts disclosedherein is better than the absolute selectivity, yield, conversion, orcombinations thereof, of the same reaction under the same conditions butcatalyzed by a corresponding catalyst. For example, in some embodimentsthe yield (e.g., C2+ yield) of desired product(s) in a reactioncatalyzed by the catalysts is greater than 10%, greater than 20%,greater than 30%, greater than 50%, greater than 75%, or greater than90%. In some embodiments, the reaction is OCM and the yield of productis greater than 10%, greater than 20%, greater than 30% or greater than40%. In other embodiments, the selectivity for product (e.g., C2+selectivity) in a reaction catalyzed by the catalysts is greater than10%, greater than 20%, greater than 30%, greater than 50%, greater than75%, or greater than 90%. In other embodiments, the conversion (e.g.,methane conversion) of reactant to product in a reaction catalyzed bythe catalysts is greater than 10%, greater than 20%, greater than 30%,greater than 50%, greater than 75%, or greater than 90%.

In certain embodiments wherein the catalysts are nanowires, themorphology of the nanowires is expected to provide for improved mixingproperties for the nanowires compared to standard colloidal (e.g., bulk)catalyst materials. The improved mixing properties are expected toimprove the performance of any number of catalytic reactions, forexample, in the area of transformation of heavy hydrocarbons wheretransport and mixing phenomena are known to influence the catalyticactivity. In other reactions, the shape of the nanowires is expected toprovide for good blending, reduce settling, and provide for facileseparation of any solid material.

In some other chemical reactions, the nanowires are useful forabsorption and/or incorporation of a reactant used in chemical looping.For example, the nanowires find utility as NO_(x) traps, in unmixedcombustion schemes, as oxygen storage materials, as CO₂ sorptionmaterials (e.g., cyclic reforming with high H₂ output) and in schemesfor conversion of water to H₂.

1. Oxidative Coupling of Methane (OCM)

As noted above, the present disclosure provides catalysts havingcatalytic activity and related approaches to catalyst design andpreparation for improving the yield, selectivity and/or conversion ofany number of catalyzed reactions, including the OCM reaction. Reactorsuseful in practice of the OCM methods described herein are known in theart and are described in PCT Pub. No. WO 2013/177433, which applicationis hereby incorporated by reference in its entirety. As mentioned above,there exists a tremendous need for catalyst technology capable ofaddressing the conversion of methane into high value chemicals (e.g.,ethylene and products prepared therefrom) using a direct route that doesnot go through syngas. Accomplishing this task will dramatically impactand redefine a non-petroleum based pathway for feedstock manufacturingand liquid fuel production yielding reductions in GHG emissions, as wellas providing new fuel sources.

Ethylene has the largest carbon footprint compared to all industrialchemical products in part due to the large total volume consumed into awide range of downstream important industrial products includingplastics, surfactants and pharmaceuticals. In 2008, worldwide ethyleneproduction exceeded 120 M metric tons while growing at a robust rate of4% per year. The United States represents the largest single producer at28% of the world capacity. Ethylene is primarily manufactured from hightemperature cracking of naphtha (e.g., oil) or ethane that is separatedfrom natural gas. The true measurement of the carbon footprint can bedifficult as it depends on factors such as the feedstock and theallocation as several products are made and separated during the sameprocess. However, some general estimates can be made based on publisheddata.

Cracking consumes a significant portion (about 65%) of the total energyused in ethylene production and the remainder is for separations usinglow temperature distillation and compression. The total tons of CO₂emission per ton of ethylene are estimated at between 0.9 to 1.2 fromethane cracking and 1 to 2 from naphtha cracking. Roughly, 60% ofethylene produced is from naphtha, 35% from ethane and 5% from otherssources (Ren, T.; Patel, M. Res. Conserv. Recycl. 53:513, 2009).Therefore, based on median averages, an estimated amount of CO₂emissions from the cracking process is 114M tons per year (based on 120Mtons produced). Separations would then account for an additional 61Mtons CO₂ per year.

The catalysts of this disclosure provide an alternative to the need forthe energy intensive cracking step. Additionally, because of the highselectivity of the catalysts, downstream separations are dramaticallysimplified, as compared to cracking which yields a wide range ofhydrocarbon products. The reaction is also exothermic so it can proceedvia an autothermal process mechanism. Overall, it is estimated that upto a potential 75% reduction in CO₂ emission compared to conventionalmethods could be achieved. This would equate to a reduction of onebillion tons of CO₂ over a ten-year period and would save over 1Mbarrels of oil per day.

The catalysts of this disclosure also permit converting ethylene intoliquid fuels such as gasoline or diesel, given ethylene's highreactivity and numerous publications demonstrating high yield reactions,in the lab setting, from ethylene to gasoline and diesel. On a lifecycle basis from well to wheel, recent analysis of methane to liquid(MTL) using F-T process derived gasoline and diesel fuels has shown anemission profile approximately 20% greater to that of petroleum basedproduction (based on a worst case scenario) (Jaramillo, P., Griffin, M.,Matthews, S., Env. Sci. Tech 42:7559, 2008). In the model, the CO₂contribution from plant energy was a dominating factor at 60%. Thus,replacement of the cracking and F-T process would be expected to providea notable reduction in net emissions, and could be produced at lower CO₂emissions than petroleum based production.

Furthermore, a considerable portion of natural gas is found in regionsthat are remote from markets or pipelines. Most of this gas is flared,re-circulated back into oil reservoirs, or vented given its low economicvalue. The World Bank estimates flaring adds 400M metric tons of CO₂ tothe atmosphere each year as well as contributing to methane emissions.The catalysts of this disclosure also provide economic and environmentalincentive to stop flaring. Also, the conversion of methane to fuel hasseveral environmental advantages over petroleum-derived fuel. Naturalgas is the cleanest of all fossil fuels, and it does not contain anumber of impurities such as mercury and other heavy metals found inoil. Additionally, contaminants including sulfur are also easilyseparated from the initial natural gas stream. The resulting fuels burnmuch cleaner with no measurable toxic pollutants and provide loweremissions than conventional diesel and gasoline in use today. In view oftheir wide range of applications, the catalysts (e.g., bulk and/ornanowires) of this disclosure can be used to not only selectivelyactivate alkanes, but also to activate other classes of inert unreactivebonds, such as C—F, C—Cl or C—O bonds. This has importance, for example,in the destruction of man-made environmental toxins such as CFCs, PCBs,dioxins and other pollutants. Accordingly, while the invention isdescribed in greater detail below in the context of the OCM reaction andthe other reactions described herein, the nanowire catalysts are not inany way limited to this or any other particular reaction.

The selective, catalytic oxidative coupling of methane to ethylene(i.e., the OCM reaction) is shown by the following reaction (1):

2CH₄+O₂→CH₂CH₂+2H₂O  (1)

This reaction is exothermic (Heat of Reaction −67 kcals/mole) andusually occurs at very high temperatures (>700° C.). During thisreaction, it is believed that the methane (CH₄) is first oxidativelycoupled into ethane (C₂H₆), and subsequently the ethane (C₂H₆) isoxidatively dehydrogenated into ethylene (C₂H₄). Because of the hightemperatures used in the reaction, it has been suggested that the ethaneis produced mainly by the coupling in the gas phase of thesurface-generated methyl (CH₃) radicals. Reactive metal oxides (oxygentype ions) are apparently required for the activation of CH₄ to producethe CH₃ radicals. The yield of C₂H₄ and C₂H₆ is limited by furtherreactions in the gas phase and to some extent on the catalyst surface. Afew of the possible reactions that occur during the oxidation of methaneare shown below as reactions (2) through (8):

CH₄→CH₃ radical  (2)

CH₃ radical→C₂H₆  (3)

CH₃ radical+2.5O₂→CO₂+1.5H₂O  (4)

C₂H₆→C₂H₄+H₂  (5)

C₂H₆+0.5O₂→C₂H₄+H₂O  (6)

C₂H₄+3O₂→2CO₂₊₂H₂O  (7)

CH₃ radical+C_(x)H_(y)+O₂→Higher HC's-Oxidation/CO₂+H₂O  (8)

With conventional heterogeneous catalysts and reactor systems, thereported performance is generally limited to <25% CH₄ conversion at <80%combined C2+ selectivity with the performance characteristics of highselectivity at low conversion, or the low selectivity at highconversion. In contrast, the catalysts of this disclosure are highlyactive and can optionally operate at a much lower temperature. In oneembodiment, the catalysts disclosed herein enable efficient conversionof methane to ethylene in the OCM reaction at temperatures less thanwhen other known catalysts are used. For example, in one embodiment, thecatalysts disclosed herein enable efficient conversion (i.e., highyield, conversion, and/or selectivity) of methane to ethylene attemperatures of less than 900° C., less than 800° C., less than 700° C.,less than 600° C., less than 550° C., or less than 500° C. In otherembodiments, the use of staged oxygen addition, designed heatmanagement, rapid quench and/or advanced separations may also beemployed.

Typically, the OCM reaction is run in a mixture of oxygen and nitrogenor other inert gas. Such gasses are expensive and increase the overallproduction costs associated with preparation of ethylene or ethane frommethane. However, the present inventors have now discovered that suchexpensive gases are not required and high yield, conversion,selectivity, etc., can be obtained when air is used as the gas mixtureinstead of pre-packaged and purified sources of oxygen and other gases.Accordingly, in one embodiment the disclosure provides a method forperforming the OCM reaction using air as the oxidizer source.

Accordingly, one embodiment of the present disclosure is a method forthe preparation of ethane and/or ethylene, the method comprisingconverting methane to ethane and/or ethylene in the presence of acatalytic material, wherein the catalytic material comprises at leastone catalyst as disclosed herein.

Accordingly, in one embodiment a stable, very active, high surface area,multifunctional catalyst is disclosed having active sites that areisolated and precisely engineered with the catalytically active metalcenters/sites in the desired proximity (see, e.g., FIG. 1) forfacilitating the OCM reaction, as well as other reactions.

The exothermic heats of reaction (free energy) follow the order ofreactions depicted above and, because of the proximity of the activesites, will mechanistically favor ethylene formation while minimizingcomplete oxidation reactions that form CO and CO₂. Representativecatalyst compositions useful for the OCM reaction include, but are notlimited to the catalyst compositions described herein, including bothbulk and nanowire morphologies.

As noted above, the presently disclosed catalysts comprise a catalyticperformance better than corresponding catalysts, for example in oneembodiment the catalytic performance of the catalysts in the OCMreaction is better than the catalytic performance of a correspondingcatalyst. In this regard, various performance criteria may define the“catalytic performance” of the catalysts in the OCM (and otherreactions). In one embodiment, catalytic performance is defined by C2+selectivity in the OCM reaction, and the C2+ selectivity of thecatalysts in the OCM reactionis >5%, >10%, >15%, >20%, >25%, >30%, >35%, >40%, >45%, >50%, >55%, >60%, >65%, >70%, >75%or >80%.

Other important performance parameters used to measure the catalysts'catalytic performance in the OCM reaction are selected from single passmethane conversion percentage (i.e., the percent of methane converted ona single pass over the catalyst or catalytic bed, etc.), reaction inletgas temperature, reaction operating temperature, total reactionpressure, methane partial pressure, gas-hour space velocity (GHSV), O₂source, catalyst stability and ethylene to ethane ratio. In certainembodiments, improved catalytic performance is defined in terms of thecatalysts' improved performance (relative to a corresponding catalyst)with respect to at least one of the foregoing performance parameters.

The reaction inlet gas temperature in an OCM reaction catalyzed by thedisclosed catalysts can generally be maintained at a lower temperature,while maintaining better performance characteristics (e.g., conversion,C2+ yield, C2+ selectivity and the like) compared to the same reactioncatalyzed by a corresponding undoped catalyst under the same reactionconditions. In certain embodiments, the inlet gas temperature in an OCMreaction catalyzed by the disclosed catalysts is <700° C., <675° C.,<650° C., <625° C., <600° C., <593° C., <580° C., <570° C., <560° C.,<550° C., <540° C., <530° C., <520° C., <510° C., <500° C., <490° C.,<480° C. or even <470° C.

The reaction operating temperature in an OCM reaction catalyzed by thedisclosed catalysts can generally be maintained at a lower temperature,while maintaining better performance characteristics compared to thesame reaction catalyzed by a corresponding catalyst under the samereaction conditions. In certain embodiments, the reaction operatingtemperature (i.e., outlet temperature) in an OCM reaction catalyzed bythe disclosed catalysts is <950° C., <925° C., <900° C., <875° C., <850°C., <825° C., <800° C., <775° C., <750° C., <725° C., <700° C., <675°C., <650° C., <625° C., <600° C., <593° C., <580° C., <570° C., <560°C., <550° C., <540° C., <530° C., <520° C., <510° C., <500° C., <490°C., <480° C., <470° C., <460° C., <450° C., <440° C., <430° C., <420°C., <410° C., <400° C.

The single pass methane conversion in an OCM reaction catalyzed by thecatalysts is also generally better compared to the single pass methaneconversion in the same reaction catalyzed by a corresponding catalystunder the same reaction conditions. For single pass methane conversionit ispreferably >5%, >10%, >15%, >20%, >25%, >30%, >35%, >40%, >45%, >50%, >55%, >60%, >65%, >70%, >75%,or even >80%.

In certain embodiments, the inlet reaction pressure in an OCM reactioncatalyzed by the catalysts is >1 atm, >1.1 atm, >1.2 atm, >1.3 atm, >1.4atm, >1.5 atm, >1.6 atm, >1.7 atm, >1.8 atm, >1.9 atm, >2 atm, >2.1atm, >2.1 atm, >2.2 atm, >2.3 atm, >2.4 atm, >2.5 atm, >2.6 atm, >2.7atm, >2.8 atm, >2.9 atm, >3.0 atm, >3.5 atm, >4.0 atm, >4.5 atm, >5.0atm, >5.5 atm, >6.0 atm, >6.5 atm, >7.0 atm, >7.5 atm, >8.0 atm, >8.5atm, >9.0 atm, >10.0 atm, >11.0 atm, >12.0 atm, >13.0 atm, >14.0atm, >15.0 atm, >16.0 atm, >17.0 atm, >18.0 atm, >19.0 atm or >20.0 atm.

In certain other embodiments, the total reaction pressure in an OCMreaction catalyzed by the catalysts ranges from about 1 atm to about 16atm, from about 1 atm to about 11 atm, from about 1 atm to about 9 atm,from about 1 atm to about 7 atm, from about 1 atm to about 5 atm, fromabout 1 atm to about 3 atm or from about 1 atm to about 2 atm.

In some embodiments, the methane partial pressure in an OCM reactioncatalyzed by the catalysts is >0.3 atm, >0.4 atm, >0.5 atm, >0.6atm, >0.7 atm, >0.8 atm, >0.9 atm, >1 atm, >1.1 atm, >1.2 atm, >1.3atm, >1.4 atm, >1.5 atm, >1.6 atm, >1.7 atm, >1.8 atm, >1.9 atm, >2.0atm, >2.1 atm, >2.2 atm, >2.3 atm, >2.4 atm, >2.5 atm, >2.6 atm, >2.7atm, >2.8 atm, >2.9 atm, >3.0 atm, >3.5 atm, >4.0 atm, >4.5 atm, >5.0atm, >5.5 atm, >6.0 atm, >6.5 atm, >7.0 atm, >7.5 atm, >8.0 atm, >8.5atm, >9.0 atm, >10.0 atm, >11.0 atm, >12.0 atm, >13.0 atm, >14.0atm, >15.0 atm, >16.0 atm, >17.0 atm, >18.0 atm, >19.0 atm or >20.0 atm.

In some embodiments, the GSHV in an OCM reaction catalyzed by thecatalystsis >10,000/hr, >15,000/hr, >20,000/hr, >30,000/hr, >50,000/hr, >75,000/hr, >100,000/hr, >120,000/hr, >130,000/hr, >150,000/hr, >200,000/hr, >250,000/hr, >300,000/hr, >350,000/hr, >400,000/hr, >450,000/hr, >500,000/hr, >750,000/hr, >1,000,000/hr, >2,000,000/hr, >3,000,000/hr,>4,000,000/hr.

In contrast to other OCM reactions, the present inventors havediscovered that OCM reactions catalyzed by the disclosed catalysts canbe performed (and still maintain high C2+ yield, C2+ selectivity,conversion, etc.) using O₂ sources other than pure O₂. For example, insome embodiments the O₂ source in an OCM reaction catalyzed by thedisclosed catalysts is air, oxygen enriched air, pure oxygen, oxygendiluted with nitrogen (or another inert gas) or oxygen diluted with CO₂.In certain embodiments, the O₂ source is O₂ dilutedby >99%, >98%, >97%, >96%, >95%, >94%, >93%, >92%, >91%, >90%, >85%, >80%, >75%, >70%, >65%, >60%, >55%, >50%, >45%, >40%, >35%, >30%, >25%, >20%, >15%, >10%, >9%, >8%, >7%, >6%, >5%, >4%, >3%, >2%or >1% with CO₂ or an inert gas, for example nitrogen.

The disclosed catalysts are also very stable under conditions requiredto perform any number of catalytic reactions, for example the OCMreaction. The stability of the catalysts is defined as the length oftime a catalyst will maintain its catalytic performance without asignificant decrease in performance (e.g., adecrease >20%, >15%, >10%, >5%, or greater than 1% in C2+ yield, C2+selectivity or conversion, etc.). In some embodiments, the disclosedcatalysts have stability under conditions required for the OCM reactionof >1 hr, >5 hrs, >10 hrs, >20 hrs, >50 hrs, >80 hrs, >90 hrs, >100hrs, >150 hrs, >200 hrs, >250 hrs, >300 hrs, >350 hrs, >400 hrs, >450hrs, >500 hrs, >550 hrs, >600 hrs, >650 hrs, >700 hrs, >750 hrs, >800hrs, >850 hrs, >900 hrs, >950 hrs, >1,000 hrs, >2,000 hrs, >3,000hrs, >4,000 hrs, >5,000 hrs, >6,000 hrs, >7,000 hrs, >8,000 hrs, >9,000hrs, >10,000 hrs, >11,000 hrs, >12,000 hrs, >13,000 hrs, >14,000hrs, >15,000 hrs, >16,000 hrs, >17,000 hrs, >18,000 hrs, >19,000hrs, >20,000 hrs, >1 yrs, >2 yrs, >3 yrs, >4 yrs or >5 yrs.

In some embodiments, the ratio of ethylene to ethane in an OCM reactioncatalyzed by the catalysts is better than the ratio of ethylene toethane in an OCM reaction catalyzed by a corresponding undoped catalystunder the same conditions. In some embodiments, the ratio of ethylene toethane in an OCM reaction catalyzed by the catalystsis >0.3, >0.4, >0.5, >0.6, >0.7, >0.8, >0.9, >1, >1.1, >1.2, >1.3, >1.4, >1.5, >1.6, >1.7, >1.8, >1.9, >2.0, >2.1, >2.2, >2.3, >2.4, >2.5, >2.6, >2.7, >2.8, >2.9, >3.0, >3.5, >4.0, >4.5, >5.0, >5.5, >6.0, >6.5, >7.0, >7.5, >8.0, >8.5, >9.0, >9.5,>10.0.

As noted above, the OCM reaction employing known catalysts suffers frompoor yield, selectivity, or conversion. In contrast, the presentlydisclosed catalysts possess a catalytic activity in the OCM reactionsuch that the yield, selectivity, and/or conversion is better than whenthe OCM reaction is catalyzed by a corresponding catalyst. In oneembodiment, the disclosure provides a catalyst having a catalyticactivity such that the conversion of methane to ethylene in theoxidative coupling of methane reaction is greater than at least 1.1times, 1.25 times, 1.50 times, 2.0 times, 3.0 times, or 4.0 times theconversion of methane to ethylene compared to the same reaction underthe same conditions but performed with a corresponding catalyst. Inother embodiments, the conversion of methane to ethylene in an OCMreaction catalyzed by the catalysts is greater than 10%, greater than20%, greater than 30%, greater than 50%, greater than 75%, or greaterthan 90%.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the yield of ethylene in the oxidativecoupling of methane reaction is greater than at least 1.1 times, 1.25times, 1.50 times, 2.0 times, 3.0 times, or 4.0 times the yield ofethylene compared to the same reaction under the same conditions butperformed with a corresponding catalyst. In other embodiments, theconversion of methane to ethylene in an OCM reaction catalyzed by thecatalytic materials is greater than 10%, greater than 20%, greater than30%, greater than 50%, greater than 75%, or greater than 90%. In someembodiments the yield of ethylene in an OCM reaction catalyzed by thecatalysts is greater than 10%, greater than 20%, greater than 30%,greater than 50%, greater than 75%, or greater than 90%.

In certain embodiments, the catalysts possess a catalytic activity inthe OCM reaction such that the yield, selectivity, and/or conversion isbetter than when the OCM reaction is catalyzed by a correspondingcatalyst. In one embodiment, the disclosure provides a catalyst having acatalytic activity such that the conversion of methane in the oxidativecoupling of methane reaction is greater than at least 1.1 times, 1.25times, 1.50 times, 2.0 times, 3.0 times, or 4.0 times the conversion ofmethane compared to the same reaction under the same conditions butperformed with a corresponding catalyst. In other embodiments, theconversion of methane in an OCM reaction catalyzed by the catalyst isgreater than 10%, greater than 15%, greater than 20%, greater than 25%,greater than 30% greater than 40%, greater than 50%, greater than 75% orgreater than 90%. In some embodiments the conversion of methane isdetermined when the catalyst is employed as a heterogeneous catalyst inthe oxidative coupling of methane at a temperature of 750° C. or less,700° C. or less, 650° C. or less or even 600° C. or less. The conversionof methane may also be determined based on a single pass of a gascomprising methane over the catalyst or may be determined based onmultiple passes over the catalyst.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the C2+ yield in the oxidative coupling ofmethane reaction is greater than at least 1.1 times, 1.25 times, 1.50times, 2.0 times, 3.0 times, or 4.0 times the C2+ yield compared to thesame reaction under the same conditions but performed with acorresponding catalyst. In some embodiments the C2+ yield in an OCMreaction catalyzed by the catalyst is greater than 10%, greater than15%, greater than 20%, greater than 25%, greater than 30%, greater than50%, greater than 75%, or greater than 90%. In some embodiments the C2+yield is determined when the catalyst is employed as a heterogeneouscatalyst in the oxidative coupling of methane at a temperature of 750°C. or less, 700° C. or less, 650° C. or less or even 600° C. or less.The C2+ yield may also be determined based on a single pass of a gascomprising methane over the catalyst or may be determined based onmultiple passes over the catalyst.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the C2+ selectivity in the oxidativecoupling of methane reaction is greater than at least 1.1 times, 1.25times, 1.50 times, 2.0 times, 3.0 times, or 4.0 times the C2+selectivity compared to the same reaction under the same conditions butperformed with a corresponding catalyst. In other embodiments, the C2+selectivity in an OCM reaction catalyzed by the catalyst is greater than10%, greater than 20%, greater than 30%, greater than 40%, greater than50%, greater than 60%, greater than 65%, greater than 75%, or greaterthan 90%. In some embodiments the C2+ selectivity is determined when thecatalyst is employed as a heterogeneous catalyst in the oxidativecoupling of methane at a temperature of 750° C. or less, 700° C. orless, 650° C. or less or even 600° C. or less. The C2+ selectivity mayalso be determined based on a single pass of a gas comprising methaneover the catalyst or may be determined based on multiple passes over thecatalyst.

In another embodiment, the disclosure provides a catalyst having acatalytic activity in the OCM reaction such that the nanowire has thesame catalytic activity (i.e., same selectivity, conversion or yield),but at a lower temperature, compared to a corresponding catalyst. Insome embodiments the catalytic activity of the catalysts in the OCMreaction is the same as the catalytic activity of a correspondingcatalyst, but at a temperature of at least 20° C. less. In someembodiments the catalytic activity of the catalysts in the OCM reactionis the same as the catalytic activity of a corresponding catalyst, butat a temperature of at least 50° C. less. In some embodiments thecatalytic activity of the catalysts in the OCM reaction is the same asthe catalytic activity of a corresponding catalyst, but at a temperatureof at least 100° C. less. In some embodiments the catalytic activity ofthe catalysts in the OCM reaction is the same as the catalytic activityof a corresponding catalyst, but at a temperature of at least 200° C.less.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the selectivity for CO or CO₂ in theoxidative coupling of methane reaction is less than at least 0.9 times,0.8 times, 0.5 times, 0.2 times, or 0.1 times the selectivity for CO orCO₂ compared to the same reaction under the same conditions butperformed with a corresponding catalyst.

In other embodiments, the above selectivity, conversion and yield valuesare determined at a temperature of less than 850° C., less than 800° C.,less than 750° C., less than 700° C. or less than 650° C.

In some other embodiments, a method for converting methane into ethaneand/or ethylene comprising use of catalyst mixture comprising two ormore catalysts is provided. For example, the catalyst mixture may be amixture of a catalyst having good OCM activity and a catalyst havinggood ODH activity. Catalysts suitable for such uses are described inmore detail above.

Typically, the OCM reaction is run in a mixture of oxygen and nitrogenor other inert gas. Such gasses are expensive and increase the overallproduction costs associated with preparation of ethylene or ethane frommethane. However, the present inventors have now discovered that suchexpensive gases are not required and high yield, conversion,selectivity, etc., can be obtained when air is used as the gas mixtureinstead of pre-packaged and purified sources of oxygen and other gases.Accordingly, in one embodiment the disclosure provides a method forperforming the OCM reaction in air by use of one or more of thedisclosed catalysts.

In addition to air or O₂ gas, the presently disclosed catalysts andassociated methods provide for use of other sources of oxygen in the OCMreaction. In this respect, an alternate source of oxygen such a CO₂,H₂O, SO₂ or SO₃ may be used either in place of, or in addition to, airor oxygen as the oxygen source. Such methods have the potential toincrease the efficiency of the OCM reaction, for example by consuming areaction byproduct (e.g., CO₂ or H₂O) and controlling the OCM exothermas described below.

As noted above, in the OCM reaction, methane is oxidatively converted tomethyl radicals, which are then coupled to form ethane, which issubsequently oxidized to ethylene. In traditional OCM reactions, theoxidation agent for both the methyl radical formation and the ethaneoxidation to ethylene is oxygen. In order to minimize full oxidation ofmethane or ethane to carbon dioxide, i.e., maximize C2+ selectivity, themethane to oxygen ratio is generally kept at 4 (i.e., full conversion ofmethane into methyl radicals) or above. As a result, the OCM reaction istypically oxygen limited and thus the oxygen concentration in theeffluent is zero.

Accordingly, in one embodiment the present disclosure provides a methodfor increasing the methane conversion and increasing, or in someembodiments, not reducing, the C2+ selectivity in an OCM reaction. Thedisclosed methods include adding to a traditional OCM catalyst anotherOCM catalyst that uses an oxygen source other than molecular oxygen. Insome embodiments, the alternate oxygen source is CO₂, H₂O, SO₂, SO₃ orcombinations thereof. For example in some embodiments, the alternateoxygen source is CO₂. In other embodiments the alternate oxygen sourceis H₂O.

Because C2+ selectivity is typically between 50% and 80% in the OCMreaction, OCM typically produces significant amounts of CO₂ as abyproduct (CO₂ selectivity can typically range from 20-50%).Additionally, H₂O is produced in copious amounts, regardless of the C2+selectivity. Therefore both CO₂ and H₂O are attractive oxygen sourcesfor OCM in an O₂ depleted environment. Accordingly, one embodiment ofthe present disclosure provides a catalyst (and related methods for usethereof) which is catalytic in the OCM reaction and which uses CO₂, H₂O,SO₂, SO₃ or another alternative oxygen source or combinations thereof asa source of oxygen. Other embodiments, provide a catalytic materialcomprising two or more catalysts, wherein the catalytic materialcomprises at least one catalyst which is catalytic in the OCM reactionand uses O₂ for at least one oxygen source and at least one catalystswhich is catalytic in the OCM reaction and uses at least of CO₂, H₂O,SO₂, SO₃ NO, NO₂, NO₃ or another alternative oxygen source. Methods forperforming the OCM reaction with such catalytic materials are alsoprovided. Such catalysts comprise any of the compositions disclosedherein and are effective as catalysts in an OCM reaction using analternative oxygen source at temperatures of 900° C. or lower, 850° C.or lower, 800° C. or lower, 750° C. or lower, 700° C. or lower or even650° C. or lower.

Examples of OCM catalysts that use CO₂ or other oxygen sources ratherthan O₂ include, but are not limited to, catalysts comprising La₂O₃/ZnO,CeO₂/ZnO, CaO/ZnO, CaO/CeO₂, CaO/Cr₂O₃, CaO/MnO₂, SrO/ZnO, SrO/CeO₂,SrO/Cr₂O₃, SrO/MnO₂, SrCO₃/MnO₂, BaO/ZnO, BaO/CeO₂, BaO/Cr₂O₃, BaO/MnO₂,CaO/MnO/CeO₂, Na₂WO₄/Mn/SiO₂, Pr₂O₃, or Tb₂O₃.

Some embodiments provide a method for performing OCM, wherein a mixtureof an OCM catalyst which use O₂ as an oxygen source (referred to hereinas an O₂—OCM catalyst) and an OCM catalyst which use CO₂ as an oxygensource (referred to herein as a CO₂—OCM catalyst) is employed as thecatalytic material, for example in a catalyst bed. Such methods havecertain advantages. For example, the CO₂—OCM reaction is endothermic andthe O₂—OCM reaction is exothermic, and thus if the right mixture and/orarrangement of CO₂—OCM and O₂—OCM catalysts is used, the methods areparticularly useful for controlling the exotherm of the OCM reaction. Insome embodiments, the catalyst bed comprises a mixture of O₂—OCMcatalyst and CO₂—OCM catalysts. The mixture may be in a ratio of 1:99 to99:1. The two catalysts work synergistically as the O₂—OCM catalystsupplies the CO₂—OCM catalyst with the necessary carbon dioxide and theendothermic nature of the C2—OCM reaction serves to control the exothermof the overall reaction. Alternatively, the CO₂ source may be externalto the reaction (e.g., fed in from a CO₂ tank, or other source) and/orthe heat required for the CO₂—OCM reaction is supplied from an externalsource (e.g., heating the reactor).

Since the gas composition will tend to become enriched in CO₂ as itflows through the catalyst bed (i.e., as the OCM reaction proceeds, moreCO₂ is produced), some embodiments of the present invention provide anOCM method wherein the catalyst bed comprises a gradient of catalystswhich changes from a high concentration of O₂—OCM catalysts at the frontof the bed to a high concentration of CO₂—OCM catalysts at the end ofthe catalyst bed.

The O₂—OCM catalyst and CO₂ OCM catalyst may have the same or differentcompositions. For example, in some embodiments the O₂—OCM catalyst andCO₂—OCM catalyst have the same composition but different morphologies(e.g., nanowire, bent nanowire, bulk, etc.). In other embodiments theO₂—OCM and the CO₂—OCM catalyst have different compositions.

Furthermore, CO₂—OCM catalysts will typically have higher selectivity,but lower yields than an O₂—OCM catalyst. Accordingly, in one embodimentthe methods comprise use of a mixture of an O₂—OCM catalyst and aCO₂—OCM catalyst and performing the reaction in O₂ deprived environmentso that the CO₂—OCM reaction is favored and the selectivity isincreased. Under appropriate conditions the yield and selectivity of theOCM reaction can thus be optimized.

In some other embodiments, the catalyst bed comprises a mixture of oneor more low temperature O₂—OCM catalyst (i.e., a catalyst active at lowtemperatures, for example less than 700° C.) and one or more hightemperature CO₂—OCM catalyst (i.e., a catalyst active at hightemperatures, for example 800° C. or higher). Here, the required hightemperature for the CO₂—OCM may be provided by the hotspots produced bythe O₂—OCM catalyst. In such a scenario, the mixture may be sufficientlycoarse such that the hotspots are not being excessively cooled down byexcessive dilution effect.

In other embodiments, the catalyst bed comprises alternating layers ofO₂—OCM and CO₂—OCM catalysts. The catalyst layer stack may begin with alayer of O₂—OCM catalyst, so that it can supply the next layer (e.g., aCO₂—OCM layer) with the necessary CO₂. The O₂—OCM layer thickness may beoptimized to be the smallest at which O₂ conversion is 100% and thus theCH₄ conversion of the layer is maximized. The catalyst bed may compriseany number of catalyst layers, for example the overall number of layersmay be optimized to maximize the overall CH₄ conversion and C2+selectivity.

In some embodiments, the catalyst bed comprises alternating layers oflow temperature O₂—OCM catalysts and high temperature CO₂—OCM catalysts.Since the CO₂—OCM reaction is endothermic, the layers of CO₂—OCMcatalyst may be sufficiently thin such that in can be “warmed up” by thehotspots of the O₂—OCM layers. The endothermic nature of the CO₂—OCMreaction can be advantageous for the overall thermal management of anOCM reactor. In some embodiments, the CO₂—OCM catalyst layers act as“internal” cooling for the O₂—OCM layers, thus simplifying therequirements for the cooling, for example in a tubular reactor.Therefore, an interesting cycle takes place with the endothermicreaction providing the necessary heat for the endothermic reaction andthe endothermic reaction providing the necessary cooling for theexothermic reaction.

Accordingly, one embodiment of the present invention is a method for theoxidative coupling of methane, wherein the method comprises conversionof methane to ethane and/or ethylene in the presence of a catalyticmaterial, and wherein the catalytic material comprises a bed ofalternating layers of O₂—OCM catalysts and CO₂—OCM catalysts. In otherembodiments the bed comprises a mixture (i.e., not alternating layers)of O₂—OCM catalysts and CO₂—OCM catalysts.

In other embodiments, the OCM methods include use of a jacketed reactorwith the exothermic O₂—OCM reaction in the core and the endothermicCO₂—OCM reaction in the mantel. In other embodiments, the unused CO₂ canbe recycled and reinjected into the reactor, optionally with therecycled CH₄. Additional CO₂ can also be injected to increase theoverall methane conversion and help reduce greenhouse gases.

In other embodiments, the reactor comprises alternating stages of O₂—OCMcatalyst beds and CO₂—OCM catalyst beds. The CO₂ necessary for theCO₂—OCM stages is provided by the O₂—OCM stage upstream. Additional CO₂may also be injected. The O₂ necessary for the subsequent O₂—OCM stagesis injected downstream from the CO₂—OCM stages. The CO₂—OCM stages mayprovide the necessary cooling for the O₂—OCM stages. Alternatively,separate cooling may be provided. Likewise, if necessary the inlet gasof the CO₂—OCM stages can be additionally heated, the CO₂—OCM bed can beheated or both.

In related embodiments, the CO₂ naturally occurring in natural gas isnot removed prior to performing the OCM, alternatively CO₂ is added tothe feed with the recycled methane. Instead the CO₂ containing naturalgas is used as a feedstock for CO₂—OCM, thus potentially saving aseparation step. The amount of naturally occurring CO₂ in natural gasdepends on the well and the methods can be adjusted accordinglydepending on the source of the natural gas.

The foregoing methods can be generalized as a method to control thetemperature of very exothermic reactions by coupling them with anendothermic reaction that uses the same feedstock (or byproducts of theexothermic reaction) to make the same product (or a related product).This concept can be reversed, i.e., providing heat to an endothermicreaction by coupling it with an exothermic reaction. This will alsoallow a higher per pass yield in the OCM reactor.

For purpose of simplicity, the above description relating to the use ofO₂—OCM and CO₂—OCM catalysts was described in reference to the oxidativecoupling of methane (OCM); however, the same concept is applicable toother catalytic reactions including but not limited to: oxidativedehydrogenation (ODH) of alkanes to their corresponding alkenes,selective oxidation of alkanes and alkenes and alkynes, etc. Forexample, in a related embodiment, a catalyst capable of using analternative oxygen source (e.g., CO₂, H₂O, SO₂, SO₃ or combinationsthereof) to catalyze the oxidative dehydrogenation of ethane isprovided. Such catalysts, and uses thereof are described in more detailbelow.

Furthermore, the above methods are applicable for creating novelcatalysts by blending catalysts that use different reactants for thesame catalytic reactions, for example different oxidants for anoxidation reaction and at least one oxidant is a byproduct of one of thecatalytic reactions. In addition, the methods can also be generalizedfor internal temperature control of reactors by blending catalysts thatcatalyze reactions that share the same or similar products but areexothermic and endothermic, respectively. These two concepts can also becoupled together.

2. Oxidative Dehydrogenation

Worldwide demand for alkenes, especially ethylene and propylene, ishigh. The main sources for alkenes include steam cracking,fluid-catalytic-cracking and catalytic dehydrogenation. The currentindustrial processes for producing alkenes, including ethylene andpropylene, suffer from some of the same disadvantages described abovefor the OCM reaction. Accordingly, a process for the preparation ofalkenes which is more energy efficient and has higher yield,selectivity, and conversion than current processes is needed. Thecatalysts disclosed herein fulfill this need and provide relatedadvantages.

In one embodiment, the catalysts are useful for the oxidativedehydrogenation (ODH) of hydrocarbons (e.g., alkanes, alkenes, andalkynes). For example, in one embodiment the catalysts are useful in anODH reaction for the conversion of ethane or propane to ethylene orpropylene, respectively. Reaction scheme (9) depicts the oxidativedehydrogenation of hydrocarbons:

C_(x)H_(y)+½O₂→C_(x)H_(y-2)+H₂O  (9)

Representative catalysts useful for the ODH reaction include, but arenot limited to any of the catalysts disclosed herein.

As noted above, improvements to the yield, selectivity, and/orconversion in the ODH reaction employing bulk catalysts are needed.Accordingly, in one embodiment, the catalysts possess a catalyticactivity in the ODH reaction such that the yield, selectivity, and/orconversion is better than when the ODH reaction is catalyzed by acorresponding catalyst. In one embodiment, the disclosure provides acatalyst having a catalytic activity such that the conversion ofhydrocarbon to alkene in the ODH reaction is greater than at least 1.1times, 1.25 times, 1.50 times, 2.0 times, 3.0 times, or 4.0 times theconversion of alkane to alkene compared to the same reaction under thesame conditions but performed with a corresponding catalyst. In otherembodiments, the conversion of alkane to alkene in an ODH reactioncatalyzed by the catalyst is greater than 10%, greater than 15%, greaterthan 20%, greater than 25%, greater than 30%, greater than 50%, greaterthan 75%, or greater than 90%.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the yield of alkene in an ODH reaction isgreater than at least 1.1 times, 1.25 times, 1.50 times, 2.0 times, 3.0times, or 4.0 times the yield of alkene compared to the same reactionunder the same conditions but performed with a corresponding catalyst.In some embodiments the yield of alkene in an ODH reaction catalyzed bythe catalyst is greater than 10%, greater than 20%, greater than 30%,greater than 50%, greater than 75%, or greater than 90%.

In another embodiment, the disclosure provides a catalyst having acatalytic activity in the ODH reaction such that the nanowire has thesame catalytic activity, but at a lower temperature, compared to acorresponding catalyst. In some embodiments the catalytic activity ofthe catalysts in the ODH reaction is the same or better than thecatalytic activity of a corresponding catalyst, but at a temperature ofat least 20° C. less. In some embodiments the catalytic activity of thecatalysts in the ODH reaction is the same or better than the catalyticactivity of a corresponding catalyst, but at a temperature of at least50° C. less. In some embodiments the catalytic activity of the catalystsin the ODH reaction is the same or better than the catalytic activity ofa corresponding catalyst, but at a temperature of at least 100° C. less.In some embodiments the catalytic activity of the catalysts in the ODHreaction is the same or better than the catalytic activity of acorresponding catalyst, but at a temperature of at least 200° C. less.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the selectivity for alkenes in an ODHreaction is greater than at least 1.1 times, 1.25 times, 1.50 times, 2.0times, 3.0 times, or 4.0 times the selectivity for alkenes compared tothe same reaction under the same conditions but performed with acorresponding catalyst. In other embodiments, the selectivity foralkenes in an ODH reaction catalyzed by the catalyst is greater than50%, greater than 60%, greater than 70%, greater than 75%, greater than80%, greater than 85%, greater than 90%, or greater than 95%.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the selectivity for CO or CO₂ in an ODHreaction is less than at least 0.9 times, 0.8 times, 0.5 times, 0.2times, or 0.1 times the selectivity for CO or CO₂ compared to the samereaction under the same conditions but performed with a correspondingcatalyst.

In one embodiment, the catalysts disclosed herein enable efficientconversion of alkane to alkene in the ODH reaction at temperatures lessthan when a corresponding catalyst is used. For example, in oneembodiment, the catalysts disclosed herein enable efficient conversion(i.e., high yield, conversion, and/or selectivity) of hydrocarbon toalkene at temperatures of less than 800° C., less than 700° C., lessthan 600° C., less than 500° C., less than 400° C., or less than 300° C.

The stability of the catalysts is defined as the length of time acatalyst will maintain its catalytic performance without a significantdecrease in performance (e.g., a decrease >20%, >15%, >10%, >5%, orgreater than 1% in ODH activity or alkene selectivity, etc.). In someembodiments, the catalysts have stability under conditions required forthe ODH reaction of >1 hr, >5 hrs, >10 hrs, >20 hrs, >50 hrs, >80hrs, >90 hrs, >100 hrs, >150 hrs, >200 hrs, >250 hrs, >300 hrs, >350hrs, >400 hrs, >450 hrs, >500 hrs, >550 hrs, >600 hrs, >650 hrs, >700hrs, >750 hrs, >800 hrs, >850 hrs, >900 hrs, >950 hrs, >1,000hrs, >2,000 hrs, >3,000 hrs, >4,000 hrs, >5,000 hrs, >6,000 hrs, >7,000hrs, >8,000 hrs, >9,000 hrs, >10,000 hrs, >11,000 hrs, >12,000hrs, >13,000 hrs, >14,000 hrs, >15,000 hrs, >16,000 hrs, >17,000hrs, >18,000 hrs, >19,000 hrs, >20,000 hrs, >1 yrs, >2 yrs, >3 yrs, >4yrs or >5 yrs.

One embodiment of the present disclosure is directed to a catalystcapable of using an alternative oxygen source (e.g., CO₂, H₂O, SO₂, SO₃or combinations thereof) to catalyze the oxidative dehydrogenation ofethane. For example, the ODH reaction may proceed according to thefollowing reaction (10):

CO₂+C_(x)H_(y)→C_(x)H_(y-2)+CO+H₂O  (10)

wherein x is an integer and Y is 2_(x)+2. Compositions useful in thisregard include Fe₂O₃, Cr₂O₃, MnO₂, Ga₂O₃, Cr/SiO₂, Cr/SO₄—SiO₂,Cr—K/SO₄—SiO₂, Na₂WO₄—Mn/SiO₂, Cr-HZSM-5, Cr/Si-MCM-41 (Cr-HZSM-5 andCr/Si-MCM-41 refer to known zeolites) and MoC/SiO₂. In some embodiments,any of the foregoing catalyst compositions may be supported on SiO₂,ZrO₂, Al₂O₃, TiO₂ or combinations thereof.

The catalysts having ODH activity with alternative oxygen sources (e.g.,CO₂, referred to herein as a CO₂—ODH catalyst) have a number ofadvantages. For example, in some embodiments a method for convertingmethane to ethylene comprises use of an O₂—OCM catalyst in the presenceof a CO₂—ODH catalyst is provided. Catalytic materials comprising atleast one O₂—OCM catalyst and at least one CO₂—ODH catalyst are alsoprovided in some embodiments. This combination of catalysts results in ahigher yield of ethylene (and/or ratio of ethylene to ethane) since theCO₂ produced by the OCM reaction is consumed and used to convert ethaneto ethylene.

In one embodiment, a method for preparation of ethylene comprisesconverting methane to ethylene in the presence of two or more catalysts,wherein at least one catalyst is an O₂—OCM catalyst and at least onecatalyst is a CO₂—ODH catalyst. Such methods have certain advantages.For example, the CO₂—ODH reaction is endothermic and the O₂—OCM reactionis exothermic, and thus if the right mixture and/or arrangement ofCO₂—ODH and O₂—OCM catalysts is used, the methods are particularlyuseful for controlling the exotherm of the OCM reaction. In someembodiments, the catalyst bed comprises a mixture of O₂—OCM catalyst andCO₂—ODH catalysts. The mixture may be in a ratio of 1:99 to 99:1. Thetwo catalysts work synergistically as the O₂—OCM catalyst supplies theCO₂—ODH catalyst with the necessary carbon dioxide and the endothermicnature of the C₂—OCM reaction serves to control the exotherm of theoverall reaction.

Since the gas composition will tend to become enriched in CO₂ as itflows through the catalyst bed (i.e., as the OCM reaction proceeds, moreCO₂ is produced), some embodiments of the present invention provide anOCM method wherein the catalyst bed comprises a gradient of catalystswhich changes from a high concentration of O₂—OCM catalysts at the frontof the bed to a high concentration of CO₂—ODH catalysts at the end ofthe catalyst bed.

The O₂—ODH catalyst and CO₂—ODH catalyst may have the same or differentcompositions. For example, in some embodiments the O₂—ODH catalyst andCO₂—ODH catalyst have the same composition but different morphologies(e.g., nanowire, bent nanowire, bulk, etc.). In other embodiments theO₂—ODH and the CO₂—ODH catalyst have different compositions.

In other embodiments, the catalyst bed comprises alternating layers ofO₂—OCM and CO₂—ODH catalysts. The catalyst layer stack may begin with alayer of O₂—OCM catalyst, so that it can supply the next layer (e.g., aCO₂—ODH layer) with the necessary CO₂. The O₂—OCM layer thickness may beoptimized to be the smallest at which O₂ conversion is 100% and thus theCH₄ conversion of the layer is maximized. The catalyst bed may compriseany number of catalyst layers, for example the overall number of layersmay be optimized to maximize the overall CH₄ conversion and C₂+selectivity.

In some embodiments, the catalyst bed comprises alternating layers oflow temperature O₂—OCM catalysts and high temperature CO₂—ODH catalysts.Since the CO₂—ODH reaction is endothermic, the layers of CO₂—ODHcatalyst may be sufficiently thin such that in can be “warmed up” by thehotspots of the O₂—OCM layers. The endothermic nature of the CO₂—ODHreaction can be advantageous for the overall thermal management of anOCM reactor. In some embodiments, the CO₂—ODH catalyst layers act as“internal” cooling for the O₂—OCM layers, thus simplifying therequirements for the cooling, for example in a tubular reactor.Therefore, an interesting cycle takes place with the endothermicreaction providing the necessary heat for the endothermic reaction andthe endothermic reaction providing the necessary cooling for theexothermic reaction.

Accordingly, one embodiment of the present invention is a method for theoxidative coupling of methane, wherein the method comprises conversionof methane to ethane and/or ethylene in the presence of a catalyticmaterial, and wherein the catalytic material comprises a bed ofalternating layers of O₂—OCM catalysts and CO₂—ODH catalysts. In otherembodiments the bed comprises a mixture (i.e., not alternating layers)of O₂—OCM catalysts and CO₂—ODH catalysts. Such methods increase theethylene yield and/or ratio of ethylene to ethane compared to otherknown methods.

In other embodiments, the OCM methods include use of a jacketed reactorwith the exothermic O₂—OCM reaction in the core and the endothermicCO₂—ODH reaction in the mantel. In other embodiments, the unused CO₂ canbe recycled and reinjected into the reactor, optionally with therecycled CH₄. Additional CO₂ can also be injected to increase theoverall methane conversion and help reduce greenhouse gases.

In other embodiments, the reactor comprises alternating stages of O₂—OCMcatalyst beds and CO₂—ODH catalyst beds. The CO₂ necessary for theCO₂—ODH stages is provided by the O₂—OCM stage upstream. Additional CO₂may also be injected. The O₂ necessary for the subsequent O₂—OCM stagesis injected downstream from the CO₂—ODH stages. The CO₂—ODH stages mayprovide the necessary cooling for the O₂—OCM stages. Alternatively,separate cooling may be provided. Likewise, if necessary the inlet gasof the CO₂—ODH stages can be additionally heated, the CO₂—ODH bed can beheated or both.

In related embodiments, the CO₂ naturally occurring in natural gas isnot removed prior to performing the OCM, alternatively CO₂ is added tothe feed with the recycled methane. Instead the CO₂ containing naturalgas is used as a feedstock for CO₂—ODH, thus potentially saving aseparation step. The amount of naturally occurring CO₂ in natural gasdepends on the well and the methods can be adjusted accordinglydepending on the source of the natural gas.

3. Carbon Dioxide Reforming of Methane

Carbon dioxide reforming (CDR) of methane is an attractive process forconverting CO₂ in process streams or naturally occurring sources intothe valuable chemical product, syngas (a mixture of hydrogen and carbonmonoxide). Syngas can then be manufactured into a wide range ofhydrocarbon products through processes such as the Fischer-Tropschsynthesis (discussed below) to form liquid fuels including methanol,ethanol, diesel, and gasoline. The result is a powerful technique to notonly remove CO₂ emissions but also create a new alternative source forfuels that are not derived from petroleum crude oil. The CDR reactionwith methane is exemplified in reaction scheme (11).

CO₂+CH₄→2CO+2H₂  (11)

Unfortunately, no established industrial technology for CDR exists todayin spite of its tremendous potential value. While not wishing to bebound by theory, it is thought that the primary problem with CDR is dueto side-reactions from catalyst deactivation induced by carbondeposition via the Boudouard reaction (reaction scheme (12)) and/ormethane cracking (reaction scheme (13)) resulting from the hightemperature reaction conditions. The occurrence of the coking effect isintimately related to the complex reaction mechanism, and the associatedreaction kinetics of the catalysts employed in the reaction.

2CO→C+CO₂  (12)

CH₄→C+2H₂  (13)

While not wishing to be bound by theory, the CDR reaction is thought toproceed through a multistep surface reaction mechanism. FIG. 3schematically depicts a CDR reaction 700, in which activation anddissociation of CH₄ occurs on the metal catalyst surface 710 to formintermediate “M-C”. At the same time, absorption and activation of CO₂takes place at the oxide support surface 720 to provide intermediate“S—CO₂”, since the carbon in a CO₂ molecule as a Lewis acid tends toreact with the Lewis base center of an oxide. The final step is thereaction between the M-C species and the activated S—CO₂ to form CO.

In one embodiment, the catalysts disclosed herein are useful ascatalysts for the carbon dioxide reforming of methane. For example, inone embodiment the catalysts are useful as catalysts in a CDR reactionfor the production of syn gas.

Improvements to the yield, selectivity, and/or conversion in the CDRreaction employing known catalysts are needed. Accordingly, in oneembodiment, the catalysts possess a catalytic activity in the CDRreaction such that the yield, selectivity, and/or conversion is betterthan when the CDR reaction is catalyzed by a corresponding catalyst. Inone embodiment, the disclosure provides a catalyst having a catalyticactivity such that the conversion of CO₂ to CO in the CDR reaction isgreater than at least 1.1 times, 1.25 times, 1.50 times, 2.0 times, 3.0times, or 4.0 times the conversion of CO₂ to CO compared to the samereaction under the same conditions but performed with a correspondingcatalyst. In other embodiments, the conversion of CO₂ to CO in a CDRreaction catalyzed by the catalyst is greater than 10%, greater than15%, greater than 20%, greater than 25%, greater than 30%, greater than50%, greater than 75%, or greater than 90%.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the yield of CO in a CDR reaction isgreater than at least 1.1 times, 1.25 times, 1.50 times, 2.0 times, 3.0times, or 4.0 times the yield of CO compared to the same reaction underthe same conditions but performed with a corresponding catalyst. In someembodiments the yield of CO in a CDR reaction catalyzed by the catalystis greater than 10%, greater than 20%, greater than 30%, greater than50%, greater than 75%, or greater than 90%.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the selectivity for CO in a CDR reaction isgreater than at least 1.1 times, 1.25 times, 1.50 times, 2.0 times, 3.0times, or 4.0 times the selectivity for CO compared to the same reactionunder the same conditions but performed with a corresponding catalyst.In other embodiments, the selectivity for CO in a CDR reaction catalyzedby the catalyst is greater than 10%, greater than 20%, greater than 30%,greater than 40%, greater than 50%, greater than 65%, greater than 75%,or greater than 90%.

In another embodiment, the disclosure provides a catalyst having acatalytic activity in a CDR reaction such that the catalyst has the sameor better catalytic activity, but at a lower temperature, compared to acorresponding. In some embodiments the catalytic activity of thecatalysts in a CDR reaction is the same or better than the catalyticactivity of a corresponding catalyst, but at a temperature of at least20° C. less. In some embodiments the catalytic activity of the catalystsin a CDR reaction is the same or better than the catalytic activity of acorresponding catalyst, but at a temperature of at least 50° C. less. Insome embodiments the catalytic activity of the catalysts in a CDRreaction is the same or better than the catalytic activity of acorresponding catalyst, but at a temperature of at least 100° C. less.In some embodiments the catalytic activity of the catalysts in a CDRreaction is the same or better than the catalytic activity of acorresponding catalyst, but at a temperature of at least 200° C. less.

In one embodiment, the catalysts disclosed herein enable efficientconversion of CO₂ to CO in the CDR reaction at temperatures less thanwhen a corresponding catalyst is used. For example, in one embodiment,the catalysts enable efficient conversion (i.e., high yield, conversion,and/or selectivity) of CO₂ to CO at temperatures of less than 900° C.,less than 800° C., less than 700° C., less than 600° C., or less than500° C.

4. Fischer-Tropsch Synthesis

Fischer-Tropsch synthesis (FTS) is a valuable process for convertingsynthesis gas (i.e., CO and H₂) into valuable hydrocarbon fuels, forexample, light alkenes, gasoline, diesel fuel, etc. FTS has thepotential to reduce the current reliance on the petroleum reserve andtake advantage of the abundance of coal and natural gas reserves.Current FTS processes suffer from poor yield, selectivity, conversion,catalyst deactivation, poor thermal efficiency and other relateddisadvantages. Production of alkanes via FTS is shown in reaction scheme(14), wherein n is an integer.

CO+2H₂→(1/n)(C_(n)H_(2n))+H₂O  (14)

In one embodiment, the catalysts are useful as catalysts in FTSprocesses. For example, in one embodiment the catalysts are useful ascatalysts in a FTS process for the production of alkanes.

Improvements to the yield, selectivity, and/or conversion in FTSprocesses employing bulk catalysts are needed. Accordingly, in oneembodiment, the catalysts possess a catalytic activity in an FTS processsuch that the yield, selectivity, and/or conversion is better than whenthe FTS process is catalyzed by a corresponding catalyst. In oneembodiment, the disclosure provides a catalyst having a catalyticactivity such that the conversion of CO to alkane in an FTS process isgreater than at least 1.1 times, 1.25 times, 1.50 times, 2.0 times, 3.0times, or 4.0 times the conversion of CO to alkane compared to the samereaction under the same conditions but performed with a correspondingcatalyst. In other embodiments, the conversion of CO to alkane in an FTSprocess catalyzed by the catalyst is greater than 10%, greater than 15%,greater than 20%, greater than 25%, greater than 30%, greater than 50%,greater than 75%, or greater than 90%.

In another embodiment, the disclosure provides a catalyst having acatalytic activity in an FTS process such that the catalyst has the sameor better catalytic activity, but at a lower temperature, compared acorresponding catalyst. In some embodiments, the catalytic activity ofthe catalysts in an FTS process is the same or better than the catalyticactivity of a corresponding catalyst, but at a temperature of at least20° C. less. In some embodiments the catalytic activity of the catalystsin an FTS process is the same or better than the catalytic activity of acorresponding catalyst, but at a temperature of at least 50° C. less. Insome embodiments the catalytic activity of the catalysts in an FTSprocess is the same or better than the catalytic activity of acorresponding catalyst, but at a temperature of at least 100° C. less.In some embodiments the catalytic activity of the catalysts in an FTSprocess is the same or better than the catalytic activity of acorresponding catalyst, but at a temperature of at least 200° C. less.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the yield of alkane in a FTS process isgreater than at least 1.1 times, 1.25 times, 1.50 times, 2.0 times, 3.0times, or 4.0 times the yield of alkane compared to the same reactionunder the same conditions but performed with a corresponding catalyst.In some embodiments the yield of alkane in an FTS process catalyzed bythe catalyst is greater than 10%, greater than 20%, greater than 30%,greater than 40%, greater than 50%, greater than 65%, greater than 75%,or greater than 90%.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the selectivity for alkanes in an FTSprocess is greater than at least 1.1 times, 1.25 times, 1.50 times, 2.0times, 3.0 times, or 4.0 times the selectivity for alkanes compared tothe same reaction under the same conditions but performed with acorresponding catalyst. In other embodiments, the selectivity foralkanes in an FTS process catalyzed by the catalyst is greater than 10%,greater than 20%, greater than 30%, greater than 50%, greater than 75%,or greater than 90%.

In one embodiment, the catalysts disclosed herein enable efficientconversion of CO to alkanes in a CDR process at temperatures less thanwhen a corresponding catalyst is used. For example, in one embodiment,the catalysts enable efficient conversion (i.e., high yield, conversion,and/or selectivity) of CO to alkanes at temperatures of less than 400°C., less than 300° C., less than 250° C., less than 200° C., less the150° C., less than 100° C. or less than 50° C.

5. Oxidation of CO

Carbon monoxide (CO) is a toxic gas and can convert hemoglobin tocarboxyhemoglobin resulting in asphyxiation. Dangerous levels of CO canbe reduced by oxidation of CO to CO₂ as shown in reaction scheme 15:

CO+½O₂→CO₂  (15)

Catalysts for the conversion of CO into CO₂ have been developed butimprovements to the known catalysts are needed. Accordingly in oneembodiment, the present disclosure provides catalysts useful ascatalysts for the oxidation of CO to CO₂.

In one embodiment, the catalysts possess a catalytic activity in aprocess for the conversion of CO into CO₂ such that the yield,selectivity, and/or conversion is better than when the oxidation of COinto CO₂ is catalyzed by a corresponding catalyst. In one embodiment,the disclosure provides a catalyst having a catalytic activity such thatthe conversion of CO to CO₂ is greater than at least 1.1 times, 1.25times, 1.50 times, 2.0 times, 3.0 times, or 4.0 times the conversion ofCO to CO₂ compared to the same reaction under the same conditions butperformed with a corresponding catalyst. In other embodiments, theconversion of CO to CO₂ catalyzed by the catalyst is greater than 10%,greater than 15%, greater than 20%, greater than 25%, greater than 30%,greater than 50%, greater than 75%, or greater than 90%.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the yield of CO₂ from the oxidation of COis greater than at least 1.1 times, 1.25 times, 1.50 times, 2.0 times,3.0 times, or 4.0 times the yield of CO₂ compared to the same reactionunder the same conditions but performed with a corresponding catalyst.In some embodiments the yield of CO₂ from the oxidation of CO catalyzedby the catalyst is greater than 10%, greater than 20%, greater than 30%,greater than 50%, greater than 75%, or greater than 90%.

In another embodiment, the disclosure provides a catalyst having acatalytic activity in an oxidation of CO reaction such that the catalysthas the same or better catalytic activity, but at a lower temperature,compared to a corresponding catalyst. In some embodiments the catalyticactivity of the catalysts in an oxidation of CO reaction is the same orbetter than the catalytic activity of a corresponding catalyst, but at atemperature of at least 20° C. less. In some embodiments the catalyticactivity of the catalysts in an oxidation of CO reaction is the same orbetter than the catalytic activity of a corresponding catalyst, but at atemperature of at least 50° C. less. In some embodiments the catalyticactivity of the catalysts in an oxidation of CO reaction is the same orbetter than the catalytic activity of a corresponding catalyst, but at atemperature of at least 100° C. less. In some embodiments the catalyticactivity of the catalysts in an oxidation of CO reaction is the same orbetter than the catalytic activity of a corresponding catalyst, but at atemperature of at least 200° C. less.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the selectivity for CO₂ in the oxidation ofCO is greater than at least 1.1 times, 1.25 times, 1.50 times, 2.0times, 3.0 times, or 4.0 times the selectivity for CO₂ compared to thesame reaction under the same conditions but performed with acorresponding catalyst. In other embodiments, the selectivity for CO₂ inthe oxidation of CO catalyzed by the catalyst is greater than 10%,greater than 20%, greater than 30%, greater than 40%, greater than 50%,greater than 65%, greater than 75%, or greater than 90%.

In one embodiment, the catalysts disclosed herein enable efficientconversion of CO to CO₂ at temperatures less than when a correspondingcatalyst is used as a catalyst. For example, in one embodiment, thecatalysts enable efficient conversion (i.e., high yield, conversion,and/or selectivity) of CO to CO₂ at temperatures of less than 500° C.,less than 400° C., less than 300° C., less than 200° C., less than 100°C., less than 50° C. or less than 20° C. Although various reactions havebeen described in detail, the disclosed catalysts are useful ascatalysts in a variety of other reactions. In general, the disclosedcatalysts find utility in any reaction utilizing a heterogeneouscatalyst and have a catalytic activity such that the yield, conversion,and/or selectivity in reaction catalyzed by the catalysts is better thanthe yield, conversion and/or selectivity in the same reaction catalyzedby a corresponding catalyst.

6. Combustion of Hydrocarbons

In another embodiment, the present disclosure provides a catalyst havingcatalytic activity in a reaction for the catalyzed combustion ofhydrocarbons. Such catalytic reactions find utility in catalyticconverters for automobiles, for example by removal of unburnedhydrocarbons in the exhaust by catalytic combustion or oxidation of sootcaptured on catalyzed particle filters resulting in reduction on dieselemissions from the engine. When running “cold”, the exhausts temperatureof a diesel engine is quite low, thus a low temperature catalyst, suchas the disclosed catalysts, is needed to efficiently eliminate allunburned hydrocarbons. In addition, in case of soot removal on catalyzedparticulate filters, intimate contact between the soot and the catalystis require; the open mesh morphology of catalyst coating is advantageousto promote such intimate contact between soot and oxidation catalyst.

In contrast to a corresponding catalyst, Applicants have found thatcertain catalysts, for example the exemplary catalysts disclosed herein,possess a catalytic activity (for example because of their morphology)in the combustion of hydrocarbons or soot such that the yield,selectivity, and/or conversion is better than when the combustion ofhydrocarbons is catalyzed by a corresponding catalyst. In oneembodiment, the disclosure provides a catalyst having a catalyticactivity such that the combustion of hydrocarbons is greater than atleast 1.1 times, 1.25 times, 1.50 times, 2.0 times, 3.0 times, or 4.0times the combustion of hydrocarbons compared to the same reaction underthe same conditions but performed with a corresponding catalyst. Inother embodiments, the total combustion of hydrocarbons catalyzed by thecatalyst is greater than 10%, greater than 20%, greater than 30%,greater than 50%, greater than 75%, or greater than 90%.

In another embodiment, the disclosure provides a catalyst having acatalytic activity such that the yield of combusted hydrocarbon productsis greater than at least 1.1 times, 1.25 times, 1.50 times, 2.0 times,3.0 times, or 4.0 times the yield of combusted hydrocarbon productscompared to the same reaction under the same conditions but performedwith a corresponding catalyst. In some embodiments the yield ofcombusted hydrocarbon products in a reaction catalyzed by the catalystis greater than 10%, greater than 20%, greater than 30%, greater than50%, greater than 75%, or greater than 90%.

The stability of the catalysts is defined as the length of time acatalyst will maintain its catalytic performance without a significantdecrease in performance (e.g., a decrease >20%, >15%, >10%, >5%, orgreater than 1% in hydrocarbon or soot combustion activity). In someembodiments, the catalysts have stability under conditions required forthe hydrocarbon combustion reaction of >1 hr, >5 hrs, >10 hrs, >20hrs, >50 hrs, >80 hrs, >90 hrs, >100 hrs, >150 hrs, >200 hrs, >250hrs, >300 hrs, >350 hrs, >400 hrs, >450 hrs, >500 hrs, >550 hrs, >600hrs, >650 hrs, >700 hrs, >750 hrs, >800 hrs, >850 hrs, >900 hrs, >950hrs, >1,000 hrs, >2,000 hrs, >3,000 hrs, >4,000 hrs, >5,000 hrs, >6,000hrs, >7,000 hrs, >8,000 hrs, >9,000 hrs, >10,000 hrs, >11,000hrs, >12,000 hrs, >13,000 hrs, >14,000 hrs, >15,000 hrs, >16,000hrs, >17,000 hrs, >18,000 hrs, >19,000 hrs, >20,000 hrs, >1 yrs, >2yrs, >3 yrs, >4 yrs or >5 yrs.

In another embodiment, the disclosure provides a catalyst having acatalytic activity in the combustion of hydrocarbons such that thecatalyst has the same or better catalytic activity, but at a lowertemperature, compared to a corresponding catalyst. In some embodimentsthe catalytic activity of the catalysts in the combustion ofhydrocarbons is the same or better than the catalytic activity of acorresponding catalyst, but at a temperature of at least 20° C. less. Insome embodiments the catalytic activity of the catalysts in thecombustion of hydrocarbons is the same or better than the catalyticactivity of a corresponding catalyst, but at a temperature of at least50° C. less. In some embodiments the catalytic activity of the catalystsin the combustion of hydrocarbons is the same or better than thecatalytic activity of a corresponding catalyst, but at a temperature ofat least 100° C. less. In some embodiments the catalytic activity of thecatalysts in the combustion of hydrocarbons is the same or better thanthe catalytic activity of a corresponding catalyst, but at a temperatureof at least 200° C. less.

7. Evaluation of Catalytic Properties

To evaluate the catalytic properties of the catalysts in a givenreaction, for example those reactions discussed above, various methodscan be employed to collect and process data including measurements ofthe kinetics and amounts of reactants consumed and the products formed.In addition to allowing for the evaluation of the catalyticperformances, the data can also aid in designing large scale reactors,experimentally validating models and optimizing the catalytic process.

One exemplary methodology for collecting and processing data is depictedin FIG. 4. Three main steps are involved. The first step (block 750)comprises the selection of a reaction and catalyst. This influences thechoice of reactor and how it is operated, including batch, flow, etc.(block 754). Thereafter, the data of the reaction are compiled andanalyzed (block 760) to provide insights to the mechanism, rates andprocess optimization of the catalytic reaction. In addition, the dataprovide useful feedbacks for further design modifications of thereaction conditions. Additional methods for evaluating catalyticperformance in the laboratory and industrial settings are described in,for example, Bartholomew, C. H. et al. Fundamentals of IndustrialCatalytic Processes, Wiley-AIChE; 2Ed (1998).

As an example, in a laboratory setting, an Altamira Benchcat 200 can beemployed using a 4 mm ID diameter quartz tube with a 0.5 mm ID capillarydownstream. Quartz tubes with 2 mm or 6 mm ID can also be used.Catalysts are tested in a number of different dilutions and amounts. Insome embodiments, the range of testing is between 10 and 300 mg. In someembodiments, the catalysts are diluted with a non-reactive diluent. Thisdiluent can be quartz (SiO₂) or other inorganic materials, which areknown to be inert in the reaction condition. The purpose of the diluentis to minimize hot spots and provide an appropriate loading into thereactor. In addition, the catalyst can be blended with lesscatalytically active components as described in more detail above.

In a typical procedure, 50 mg is the total charge of catalyst,optionally including diluent. On either side of the catalysts a smallplug of glass wool is loaded to keep the catalysts in place. Athermocouple is placed on the inlet side of the catalyst bed into theglass wool to get the temperature in the reaction zone. Anotherthermocouple can be placed on the downstream end of the catalyst bedinto the catalyst bed itself to measure the exotherms, if any.

When blending the catalyst with diluent, the following exemplaryprocedure may be used: x (usually 10-50) mg of the catalyst (either bulkor nanowire catalyst) is blended with (100-x) mg of diluent. Thereafter,about 2 ml of ethanol or water is added to form a slurry mixture, whichis then sonicated for about 10 minutes. The slurry is then dried in anoven at about 100-140° C. for 2 hours to remove solvent. The resultingsolid mixture is then scraped out and loaded into the reactor betweenthe plugs of quartz wool.

Once loaded into the reactor, the reactor is inserted into the Altamirainstrument and furnace and then a temperature and flow program isstarted. In some embodiment, the total flow is 50 to 100 sccm of gasesbut this can be varied and programmed with time. In one embodiment, thetemperatures range from 400° C. to 900° C. The reactant gases compriseair or oxygen (diluted with nitrogen or argon) and methane in the caseof the OCM reaction and gas mixtures comprising ethane and/or propanewith oxygen for oxidative dehydrogenation (ODH) reactions. Other gasmixtures can be used for other reactions.

The primary analysis of these oxidation catalysis runs is the GasChromatography (GC) analysis of the feed and effluent gases. From theseanalyses, the conversion of the oxygen and alkane feed gases can easilybe attained and estimates of yields and selectivities of the productsand by-products can be determined.

The GC method developed for these experiments employs up to 4 columnsand up to 2 detectors and a complex valve switching system to optimizethe analysis. Specifically, a flame ionization detector (FID) is usedfor the analysis of the hydrocarbons only. It is a highly sensitivedetector that produces accurate and repeatable analysis of methane,ethane, ethylene, propane, propylene and all other simple alkanes andalkenes up to five carbons in length and down to ppm levels.

There can be two columns in series to perform this analysis, the firstis a stripper column (alumina) which traps polar materials (includingthe water by-product and any oxygenates generated) until back-flushedlater in the cycle. The second column associated with the FID is acapillary alumina column known as a PLOT column which performs theactual separation of the light hydrocarbons. The water and oxygenatesare not analyzed in this method.

For the analysis of the light non-hydrocarbon gases, one or more ThermalConductivity Detectors (TCD) may be employed which can also employ twocolumns to accomplish its analysis. The target molecules for thisanalysis are CO₂, ethylene, ethane, hydrogen, oxygen, nitrogen, methaneand CO. The two columns used here are a porous polymer column known asthe Hayes Sep N which performs some of the separation for the CO₂,ethylene and ethane. The second column is a molecular sieve column whichuses size differentiation to perform the separation. It is responsiblefor the separation of H₂, O₂, N₂, methane and CO.

There is a sophisticated and timing sensitive switching between thesetwo columns in the method. In the first 2 minutes or so, the two columnsare operating in series but at about 2 minutes, the molecular sievecolumn is by-passed and the separation of the first 3 components iscompleted. At about 5-7 minutes, the columns are then placed back inseries and the light gases come off of the sieve according to theirmolecular size.

The end result is an accurate analysis of all of the aforementionedcomponents from these fixed-beds, gas phase reactions. Analysis of otherreactions and gases not specifically described above can be performed ina similar manner known to those of skill in the art.

8. Downstream Products

As noted above, the catalysts disclosed herein are useful in reactionsfor the preparation of a number of valuable hydrocarbon compounds. Forexample, in one embodiment the catalysts are useful for the preparationof ethylene from methane via the OCM reaction. In another embodiment,the catalysts are useful for the preparation of ethylene or propylenevia oxidative dehydrogenation of ethane or propane respectively.Ethylene and propylene are valuable compounds which can be convertedinto a variety of consumer products. For example, as shown in FIG. 5,ethylene can be converted into many various compounds including lowdensity polyethylene, high density polyethylene, ethylene dichloride,ethylene oxide, ethylbenzene, linear alcohols, vinyl acetate, alkanes,alpha olefins, various hydrocarbon-based fuels, ethanol and the like.These compounds can then be further processed using methods well knownto one of ordinary skill in the art to obtain other valuable chemicalsand consumer products (e.g., the downstream products shown in FIG. 5).Propylene can be analogously converted into various compounds andconsumer goods including polypropylenes, propylene oxides, propanol, andthe like.

Accordingly, in one embodiment the invention is directed to a method forthe preparation of C₂ hydrocarbons via the OCM reaction, the methodcomprises contacting a catalyst as described herein with a gascomprising methane. In some embodiments the C₂ hydrocarbons are selectedfrom ethane and ethylene. In other embodiments the disclosure provides amethod of preparing downstream products of ethylene. The methodcomprises converting ethylene into a downstream product of ethylene,wherein the ethylene has been prepared via a catalytic reactionemploying a catalyst disclosed herein (e.g., OCM). In some embodiments,the downstream product of ethylene is low density polyethylene, highdensity polyethylene, ethylene dichloride, ethylene oxide, ethylbenzene,ethanol or vinyl acetate from ethylene, wherein the ethylene has beenprepared as described above. In other embodiments, the downstreamproduct of ethylene is natural gasoline. In still other embodiments, thedownstream product of ethylene comprises 1-hexene, 1-octene, hexane,octane, benzene, toluene, xylene or combinations thereof.

In another embodiment, a process for the preparation of ethylene frommethane comprising contacting a mixture comprising oxygen and methane ata temperature below 900° C., below 850° C., below 800° C., below 750°C., below 700° C. or below 650° C. with a catalyst as disclosed hereinis provided.

In another embodiment, the disclosure provides a method of preparing aproduct comprising low density polyethylene, high density polyethylene,ethylene dichloride, ethylene oxide, ethylbenzene, ethanol or vinylacetate, alkenes, alkanes, aromatics, alcohols, or mixtures thereof. Themethod comprises converting ethylene into low density polyethylene, highdensity polyethylene, ethylene dichloride, ethylene oxide, ethylbenzene,ethanol or vinyl acetate, wherein the ethylene has been prepared via acatalytic reaction employing a catalyst for example any of the exemplarycatalysts disclosed herein.

In more specific embodiments of any of the above methods, the ethyleneis produced via an OCM or ODH reaction or combinations thereof.

In one particular embodiment, the disclosure provides a method ofpreparing a downstream product of ethylene and/or ethane, wherein thedownstream product is a hydrocarbon fuel. For example, the downstreamproduct of ethylene may be a hydrocarbon fuel such as natural gasolineor a C₄-C₁₄ hydrocarbon, including alkanes, alkenes and aromatics. Somespecific examples include 1-butene, 1-hexene, 1-octene, hexane, octane,benzene, toluene, xylenes and the like. The method comprises convertingmethane into ethylene, ethane or combinations thereof by use of acatalyst, for example any of the catalysts disclosed herein, and furtheroligomerizing the ethylene and/or ethane to prepare a downstream productof ethylene and/or ethane. For example, the methane may be converted toethylene, ethane or combinations thereof via the OCM reaction asdiscussed above.

As depicted in FIG. 6, the method begins with charging methane (e.g., asa component in natural gas) into an OCM reactor. The OCM reaction maythen be performed utilizing a catalyst under any variety of conditions.Water and CO₂ are optionally removed from the effluent and unreactedmethane is recirculated to the OCM reactor.

Ethylene is recovered and charged to an oligomerization reactor.Optionally the ethylene stream may contain CO₂, H₂O, N₂, ethane, C₃'sand/or higher hydrocarbons. Oligomerization to higher hydrocarbons(e.g., C₄-C₁₄) then proceeds under any number of conditions known tothose of skill in the art. For example oligomerization may be effectedby use of any number of catalysts known to those skilled in the art.Examples of such catalysts include catalytic zeolites, crystallineborosilicate molecular sieves, homogeneous metal halide catalysts, Crcatalysts with pyrrole ligands or other catalysts. Exemplary methods forthe conversion of ethylene into higher hydrocarbon products aredisclosed in the following references: Catalysis Science & Technology(2011), 1(1), 69-75; Coordination Chemistry Reviews (2011), 255(7-8),861-880; Eur. Pat. Appl. (2011), EP 2287142 A1 20110223; Organometallics(2011), 30(5), 935-941; Designed Monomers and Polymers (2011), 14(1),1-23; Journal of Organometallic Chemistry 689 (2004) 3641-3668;Chemistry—A European Journal (2010), 16(26), 7670-7676; Acc. Chem. Res.2005, 38, 784-793; Journal of Organometallic Chemistry, 695 (10-11):1541-1549 May 15 2010; Catalysis Today Volume 6, Issue 3, January 1990,Pages 329-349; U.S. Pat. Nos. 5,968,866; 6,800,702; 6,521,806;7,829,749; 7,867,938; 7,910,670; 7,414,006 and Chem. Commun., 2002,858-859, each of which are hereby incorporated in their entirety byreference.

In certain embodiments, the exemplary OCM and oligomerization modulesdepicted in FIG. 6 may be adapted to be at the site of natural gasproduction, for example a natural gas field. Thus the natural gas can beefficiently converted to more valuable and readily transportablehydrocarbon commodities without the need for transport of the naturalgas to a processing facility.

Referring to FIG. 6, “natural gasoline” refers to a mixture ofoligomerized ethylene products. In this regard, natural gasolinecomprises hydrocarbons containing 5 or more carbon atoms. Exemplarycomponents of natural gasoline include linear, branched or cyclicalkanes, alkenes and alkynes, as well as aromatic hydrocarbons. Forexample, in some embodiments the natural gasoline comprises 1-pentene,1-hexene, cyclohexene, 1-octene, benzene, toluene, dimethyl benzene,xylenes, napthalene, or other oligomerized ethylene products orcombinations thereof. In some embodiments, natural gasoline may alsoinclude C3 and C4 hydrocarbons dissolved within the liquid naturalgasoline. This mixture finds particular utility in any number ofindustrial applications, for example natural gasoline is used asfeedstock in oil refineries, as fuel blend stock by operators of fuelterminals, as diluents for heavy oils in oil pipelines and otherapplications. Other uses for natural gasoline are well-known to those ofskill in the art.

The following examples are provided for purposes of illustration, notlimitation.

EXAMPLES Example 1 Preparation of Exemplary Bulk Catalysts

Equimolar aqueous solutions of strontium nitrate, neodymium nitrate, anderbium nitrate are prepared. Aliquots of each solution are mixedtogether to prepare a desired formulation of Er_(x)Nd_(y)Sr_(z) wherex,y,z represent mole fractions of total metal content in moles.Representative examples of formulations are: Er₅₀Nd₃₀Sr₂₀, Er₅₂Nd₄₅Sr₀₅,Er₇₅Nd₂₂Sr₀₃, and the like. A solution of citric acid is added to themetal salt mixture so that citric acid mole/metal mole ratio is 3:1.Ethylene glycol is then added to the citric acid/metal salt solution sothat the ethylene glycol/citric acid mole ratio is 1:1. The solution isstirred at room temperature for 1 h. The solution is then placed in a130° C. oven for 15 h to remove water and to promote resin formation.After 15 h, a hard dark resin is observed. The resin is placed in afurnace and heated to 500° C. for 8 h. The remaining material is heatedto 650° C. for 2 h to yield the desired product.

Catalysts comprising support materials can also be prepared bycoprecipitation according to the above method. For example, rare earthoxides on MgO, CaO or AlPO₄ supports are prepared in an analogousmanner. Specific examples include, Er/Nd/Sr/CaO (i.e., a catalystcomprising Er, Nd, and Sr on a CaO support).

Other bulk catalysts are prepared according to an analogous procedure.

Example 2 Preparation of Exemplary Doped Catalyst

3.0 g of Er₂O₃ bulk from Alfa Chemicals is slurried in a solution formedby dissolving 0.378 g of Sr(NO₃)₂ in about 20 ml of DI water. The slurryis stirred at room temperature for about 30 minutes to ensure that theSr(NO₃)₂ dissolves. The slurry is then moved to an evaporating dish andplaced into an oven at 100-140° C. for 2-3 hours to ensure dryness. Thesolids are then calcined in a furnace by ramping up to 350° C. at 5°C./min and holding for 2 hours and then ramping again at the same rateto 700° C. and holding for 4 hours. It is then cooled to roomtemperature, ground and sieved to a particle size range of 180 μm to 250μm.

Catalysts comprising different dopants are prepared according to theabove general procedure.

Example 3 Preparation of Exemplary Nanowires Catalysts

Phage is prepared as described in U.S. Pub. No. 2012/004124623, the fulldisclosure of which is incorporated herein by reference. 23 ml of 2.5e12 pfu solution of phages is mixed in a 40 ml glass bottle with 0.046ml of 0.1 M ErCl₃ aqueous solution and left incubating for 16 h. Afterthis incubation period, a slow multistep addition is conducted with 1.15ml of 0.05 M ErCl₃ solution and 1.84 ml of 0.3 M NH₄OH. This addition isconducted in six hours and twenty steps. The reaction mixture is leftstirring another 2 h at room temperature. After that time the suspensionis centrifuged in order to separate the solid phase from the liquidphase. The precipitated material is then resuspended in 5 ml of waterand centrifuged in order to further remove un-reacted species. A finalwash is conducted with 2 ml ethanol. The gel-like product remaining isthen dried for 30 minutes at 110° C. in a vacuum oven.

The dried product is then calcined in a muffle furnace using a steprecipe (load in the furnace at room temperature, ramp to 200° C. with 3°C./min rate, dwell for 120 min, ramp to 400° C. with 3° C./min rate,dwell for 120 min, cool to room temperature). The calcined product isthen ground to a fine powder.

5 mg of the calcined product are impregnated with 0.015 ml Sr(NO₃)₂ 0.1Maqueous solution. Powder and solution is mixed on hot plate at 90° C.until a paste is formed. The paste is then dried for 1 h at 120° C. in avacuum oven and finally calcined in a muffle oven in air. (load in thefurnace at room temperature, ramp to 200° C. with 3° C./min rate, dwellfor 120 min, ramp to 400° C. with 3° C./min rate, dwell for 120 min,ramp to 500° C. with 3° C./min rate, dwell for 120 min, cool to roomtemperature). The nanowires obtained typically have a “bent” morphology(i.e., ratio of effective length to actual length of less than 1).

Other phage-based nanowires are prepared according to an analogousmethod.

Example 4 Exemplary Synthesis of Nanowires

Er (NO₃)₃.6H₂O (10.825 g) is added to 250 mL distilled water and stirreduntil all solids are dissolved. Concentrated ammonium hydroxide (4.885mL) is added to this mixture and stirred for at least one hour resultingin a white gel. This mixture is transferred equally to 5 centrifugetubes and centrifuged for at least 15 minutes. The supernatant isdiscarded and each pellet is rinsed with water, centrifuged for at least15 minutes and the supernatant is again discarded.

The resulting pellets are all combined, suspended in distilled water(125 mL) and heated at 105° C. for 24 hours. The erbium hydroxide isisolated by centrifugation and suspended in ethanol (20 mL). The ethanolsupernatant is concentrated and the product is dried at 65° C. until allethanol is removed.

The erbium hydroxide nanowires prepared above are calcined by heating at100° C. for 30 min., 400° C. for 4 hours and then 550° C. for 4 hours toobtain the Er₂O₃ nanowires. The nanowires obtained are substantiallystraight (i.e., ratio of effective length to actual length of about 1).

Other nanowires having different elemental compositions are preparedaccording to the above general procedure or other procedures known inthe art.

Example 5 OCM Activity of Exemplary Catalysts

Exemplary catalysts selected catalysts from those presented in tables1-20, were tested for their OCM performance parameters according to thegeneral procedures above. In particular, the methane conversion and C2+selectivities were measured at the lowest temperature required to obtain˜>50% C2+ selectivity (condition A), and at the temperature whichresults in maximum C2+ selectivity (condition B). All catalysts undercondition A showed C2+ selectivities and methane conversions greaterthan 50% and 15%, respectively, while providing C2+ selectivitiesgreater than 55% and in most cases greater than 60%, while providingmethane conversions greater than 18% and in most cases greater than 20%.It was noted that certain catalysts resulted in the almost total absenceof reforming of methane to CO and H₂.

Example 6 Measurement of OCM Activity of Exemplary Catalysts

A flow reactor having an inner diameter of 4 mm is obtained fromAltamira Instruments (Pittsburgh, Pa.). The reactor has a quartz tubethat is loaded with 50-100 mg of catalyst to be tested. The reactor isrun with 54 sccm (standard cubic centimeters per minute) of methane and46 sccm of air. The temperature is varied over a range of 400-750° C.and gases are sent to a process gas chromatograph (GC) for analysis ofall components. Methane is partially converted and the C₂ and C₃selectivity and C₂ and C₃ yields are calculated from the raw GC data.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet, includingU.S. Provisional Application No. 61/988,063, are incorporated herein byreference, in their entireties. Aspects of the embodiments can bemodified, if necessary to employ concepts of the various patents,applications and publications to provide yet further embodiments. Theseand other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

LENGTHY TABLES The patent application contains a lengthy table section.A copy of the table is available in electronic form from the USPTO website(https://seqdata.uspto.gov/?pageRequest=docDetail&DocID=US20200368725A1).An electronic copy of the table will also be available from the USPTOupon request and payment of the fee set forth in 37 CFR 1.19(b)(3).

1. A method for conversion of methane to C2+ hydrocarbons, the methodcomprising contacting a catalyst with a gas comprising methane, thecatalyst comprising: a base material comprising an oxide of two or morelanthanide elements; and a dopant combination selected from the groupconsisting of Sr/Sm, Sr/Gd, Sr/Dy, Sr/Er, Sr/Lu, Sr/Ba/B, Ba/Sr, Sr/K,Sr/Ga/Mg, Sr/Y, Sr/B/Y, Sr/Al, Sr/Ba/W, Sr/W/B and Sr/Ba/W/B, providedthat one of the lanthanide elements is not lanthanum when anotherlanthanide element is neodymium.
 2. The method of claim 1, wherein themethane is converted to C2+ hydrocarbons by an oxidative coupling ofmethane (OCM) reaction.
 3. The method of claim 1, wherein the gasfurther comprises an oxidant source.
 4. The method of claim 3, whereinthe oxidant source is a gas enriched for oxygen.
 5. The method of claim3, wherein the oxidant source is air.
 6. The method of claim 1, whereinthe method is performed in the presence of ethane.
 7. The method ofclaim 1, wherein the oxide has the following formula (III):Ln1_(a) Ln2_(b) Ln3_(d) Ln4_(e) Ln5_(f)O_(c)  (III) wherein: Ln1, Ln2,Ln3, Ln4 and Ln5 are independently different lanthanide elements; O isoxygen; a and c are each independently numbers greater than 0; and b, d,e, and f are independently 0 or a number greater than
 0. 8. The methodof claim 1, wherein the catalyst comprises a C₂+ selectivity of greaterthan 50% and a methane conversion of greater than 20% when the catalystis contacted with the gas at a temperature of 750° C. or less.
 9. Themethod of claim 8, wherein the catalyst further comprises a C2+ yieldgreater than 10% when the catalyst is contacted with the gas at atemperature of 750° C. or less.
 10. The method of claim 9, wherein themethane conversion, C₂₊ selectivity, or C2+ yield, or combinationsthereof, are measured in a 4 millimeter inner diameter tube with amethane to oxygen ratio of 5.5:1 using air as an oxidant, wherein thetemperature is 650° C.
 11. A method for conversion of methane to C2+hydrocarbons, the method comprising contacting a catalyst with a gascomprising methane, the catalyst comprising a Group 4 or lanthanideoxide in combination with an alkaline earth metal dopant selected fromthe group consisting of Ba/W, Ba/B, Ba/Sr, Ba/Ce, Ba/Hf, Y/Ba, Ca/B,Sr/Ba/W, Ba/W/B, Sr/Ba/B and Sr/Ba/W/B.
 12. The method of claim 11,wherein the methane is converted to C2+ hydrocarbons by an oxidativecoupling of methane (OCM) reaction.
 13. The method of claim 11, whereinthe gas further comprises an oxidant source.
 14. The method of claim 13,wherein the oxidant source is a gas enriched for oxygen.
 15. The methodof claim 13, wherein the oxidant source is air.
 16. The method of claim11, wherein the method is performed in the presence of ethane.
 17. Themethod of claim 11, wherein the dopant is Ba/W, Sr/Ba/W or Sr/Ba/W/B.18. The method of claim 11, wherein the catalyst comprises one of thefollowing compositions: Ba/W/Nd₂O₃ or Ba/W/Er₂O₃.
 19. The method ofclaim 11, wherein the catalyst comprises a C₂+ selectivity of greaterthan 50% and a methane conversion of greater than 20% when the catalystis contacted with the gas at a temperature of 750° C. or less.
 20. Themethod of claim 19, wherein the catalyst further comprises a C2+ yieldgreater than 10% when the catalyst is contacted with the gas at atemperature of 750° C. or less.
 21. The method of claim 20, wherein themethane conversion, C₂₊ selectivity, or C2+ yield, or combinationsthereof, are measured in a 4 millimeter inner diameter tube with amethane to oxygen ratio of 5.5:1 using air as an oxidant, wherein thetemperature is 650° C.
 22. A method for conversion of methane to C2+hydrocarbons, the method comprising contacting a catalyst with a gascomprising methane, the catalyst comprising a mixed oxide base materialand a dopant combination, the mixed oxide comprising erbium (Er) and atleast one further lanthanide element, the dopant combination selectedfrom the group consisting of Sr/Sm, Sr/Gd, Sr/Dy, Sr/Er, Sr/Lu, Sr/Ba/B,Ba/B, Ba/Sr, Er/W, Sr/K, Ba/Ce, Ba/Hf, Ga/Mg, Mg/Er, Y/Ba, Sr/Ga/Mg,Sr/Y, Sr/B/Y, Ca/B, Sr/Al, Ba/W, B/W, Sr/Ba/W, Sr/W/B, Ba/W/B andSr/Ba/W/B.
 23. The method of claim 22, wherein the methane is convertedto C2+ hydrocarbons by an oxidative coupling of methane (OCM) reaction.24. The method of claim 22, wherein the gas further comprises an oxidantsource.
 25. The method of claim 24, wherein the oxidant source is a gasenriched for oxygen.
 26. The method of claim 24, wherein the oxidantsource is air.
 27. The method of claim 22, wherein the method isperformed in the presence of ethane.
 28. The method of claim 22, whereinthe mixed oxide comprises a physical blend of Er, or an oxidized formthereof, and the further lanthanide element, or an oxidized formthereof.
 29. The method of claim 28, wherein the mixed oxide has thefollowing formula (I):Ln_(x)Er_(y)O_(z)  (I) wherein: Ln is the lanthanide element; Er iserbium; O is oxygen; and x, y and z are each independently numbersgreater than 0, wherein x, y and z are selected such that the overallcharge of the catalyst is about
 0. 30. The method of claim 29, whereinx, y and z are selected such that z is from 150% to 200% of the sum of xand y.
 31. The method of claim 29, wherein the mixed oxide is LnErO₃ orLn₃ErO₆.
 32. The method of claim 22, wherein the catalyst comprises aC2+ selectivity of greater than 50% and a methane conversion of greaterthan 20% when the catalyst is contacted with the gas at a temperature of750° C. or less.
 33. The method of claim 32, wherein the catalystfurther comprises a C2+ yield greater than 10% when the catalyst iscontacted with the gas at a temperature of 750° C. or less.
 34. Themethod of claim 33, wherein the methane conversion, C₂₊ selectivity, orC2+ yield, or combinations thereof, are measured in a 4 millimeter innerdiameter tube with a methane to oxygen ratio of 5.5:1 using air as anoxidant, wherein the temperature is 650° C.